I've posted an outline of the Scriptures based on St. Thomas' Principium Biblicum. I have been unable to find an english translation of the work, so maybe I will post my own soon. Certainly I will begin to comment on the outline.

UPDATE: I've posted my translation of the work.
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From St. Thomas’ treatment of God’s goodness, we know:

1. that the account of goodness from created things belongs also to God;
2. that the account of goodness is not said in the same way of created and uncreated things; and
3. that the way in which God is good exceeds the way in which anything we can experience directly is good.¹

Far from destroying the mystery of God, this knowledge intensifies it by pointing out that God’s goodness exceeds any goodness we can directly know in created things. Thus the believer’s possible objection against pursuing formal theology because it infringes upon the ineffability of God is proven blasphemous. For if this opposition were true, God must be such that we are capable of comprehending Him and His attributes. Theology, on the contrary, proves this impious notion false by demonstrating that the attributes of creatures bear an analogous similarity to the attributes of God, which cannot by fully understood by our intellects. The security of God’s transcendence is not a question of the amount of knowledge possible, as if more knowledge would encroach His mystery; the limitation of theology, rather, comes from the kind of knowledge that is possible of God in this life. Therefore, we should never fear that theology, however formal, precise and thorough, will lead to a smug satisfaction in having comprehended God. Instead, we should strive to know as much as we can about the Highest Subject and stand in awe at the mystery uncovered.

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1. c.f. S.T., 1, q.XII, a.12

These three aspects of knowledge by analogy are present in St. Thomas’ treatment of God’s goodness. St. Thomas prefaces the discussion with a treatment of goodness in general.¹ The notion of goodness as being insofar as it is appetible must be abstracted from creatures. This treatment is necessary to clarify the meaning of goodness before St. Thomas asks whether goodness belongs to God. That he does clarify goodness from the standpoint of knowledge from creatures, moreover, shows that goodness attributed to God falls under the same general notion of appetible being. This account of goodness is as suitably applied to God as to creatures. Therefore, if we show that God is good, this is not a meaningless phrase, nor a pure equivocation, but actually provides some positive knowledge of God, because both uses of “good” stem from a common principle: being as desired.

St. Thomas proves that goodness belongs to God by comparing effects to their cause. Every thing desires its own perfection. But the perfection of an effect is participation in its cause, since agents make things like themselves. Therefore, the perfection of every agent is desirable by the effect. But God was shown to be the agent cause of all beings.² Therefore, God is appetible, and goodness, as understood in the general account, belongs to Him.

If the same notion of goodness is applied to God as to creatures, how can we understand that this analogy is not identity, that is, that created goodness is not the same as uncreated goodness? The answer lies in the formulation of goodness, desirable being. For since God is not in a genus with any creature,³ being is said equivocally of uncreated and created being. Therefore, although the formulation of goodness is the same in either case, it is applied equivocally to God and creatures. “Good,” however, like “healthy,” is not used purely equivocally, for there is a common principle for using the same word of God and creatures, namely the formulation of goodness explained in Question 5.

Since there is a common principle of using “good,” we can have positive knowledge that God is good. Yet, since this principle is based on a likeness of cause and effect, not an identity, St. Thomas is justified in saying that, “we are not able to consider about God how He is, but rather how He is not.”⁴ For after explaining that the account of goodness we know from created things applies to God in Article I, St. Thomas spends the rest of Question VI explaining that God’s goodness exceeds any creature’s goodness. First, St. Thomas sets the goodness of God apart from all other goods by declaring that God is the highest good.⁵ God was proven to be good by being an agent cause, which necessarily has the perfections of its effects. But God is also not in a genus with created things. Therefore, God is an equivocal cause, so that He has the desirable perfections of His creation in a more excellent way than created things have them. Although the same account of goodness applies to God as to creatures, whatever way a creature is good by having a desirable perfection, God is good in a higher sense by having the same perfection in a more excellent way. Furthermore, St. Thomas goes on to point out that only God has goodness by His essence.⁶ Since His essence is incomprehensible to finite intellects, certainly His goodness is likewise unable to be grasped in itself. He then shows that created goodness emanates from God but is not simply a formal sharing in the one goodness of God,⁷ further clarifying that likeness is not identity. Although God’s goodness is not an entirely empty notion to us because of the similarity to created goodness, the entire treatment has done more to show how created goodness and God’s goodness differ than how they are similar.

The order among analogous uses of a word helps explain the compatibility of knowledge and mystery. St. Thomas has demonstrated that God is good through the similarity of cause and effect. Therefore, since goodness is in God as in a cause, “good” is said primarily of God and secondarily of creatures. But since we came to the general account of goodness through creatures, goodness of creatures is more known to us. In fact, since we have no direct experience of the creator, God’s goodness is not known directly at all. There is no phantasm of God, so the intellect has no object from which to abstract a direct concept of Him. We can know the existence of prime matter through analogy without being able to comprehend it; similarly, we can know some attributes of God without being able to comprehend their full meaning. In both cases there is true knowledge. It is only denied that we can have essential knowledge: not of prime matter because it lacks intelligibility, and not of God because His intelligibility exceeds our way of knowing.

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1. c.f. S.T., 1, q.V
2. c.f. S.T., 1, q.II, a.3
3. c.f. S.T., 1, q.III, a.5
4. S.T., 1, q.III, praemium
5. c.f. S.T., 1, q.VI, a.2
6. ibid., a.3
7. ibid., a.4

There are three things to note about knowledge by analogy in general before discussing knowledge of God by analogy to creatures. First, an analogy is a means to real knowledge of a thing. In every analogy something is known by comparison to something else to which it has a similarity. Since they have a real similarity, what is being said about them is not a pure equivocation. Unlike “bark of a tree” and “bark of a dog,” which are merely the same sounds used to signify different ideas, terms used analogously can be reduced to one principle. For example, we say “healthy” of a fit man, a nourishing steak, and a robust complexion. This is not simply the use of the same sound to signify completely different ideas - there is one reason for using “healthy” in all cases, that it signifies some relation to well-being. Therefore, calling a piece of dead meat healthy is actually informative in light of the already known healthiness of a man.

Second, an analogy is not identity. However real the similarity may be between significations, they still are not the same significations. The “healthy” said of man is not the same as the one said of steak or of color. Although there is one principle of all uses of the word, the relation to well-being, each case employs a different relation. The man is healthy, because he has health formally in him; the steak is healthy because it has the power to be a material and agent cause of well-being in something else; complexion is healthy because it is an effect of well-being. Thus, the analogous uses of a word are neither purely equivocal nor purely univocal.

Third, there may be an order among analogous senses of a word. Since formal well-being is the final cause toward which healthy agents and matter are ordered, and since a healthy complexion is an accidental consequence of a healthy man, “healthy” is primarily applied to a man. Nevertheless, a derivative use may be more known to us than a more primary use. For example, we use a healthy complexion as a sign of a healthy man because it is more obvious to us. This order of intelligibility, according to nature or according to us, is especially clear in those cases in which we can know fully one use of a word but not another. For example, we know prime matter by an analogy with the matter of an artifact:

The underlying nature, however, is understandable according to analogy. For as bronze is to statue or as timber is to bed or as matter and the formless before it takes on form is to whatever else has form, so is this underlying nature to substance and “this something” and a being.¹

We know that matter which underlies substantial change exists because we know matter which similarly underlies accidental change. Still, we can have no direct experience of prime matter, since in itself it is entirely without form and lacks intelligibility. Therefore, when we use “matter” to signify prime matter, we do not have comprehension of what that signification means. We only know that prime matter has to substantial form, which is known, a similar relationship as that of secondary matter to accidental form, which are also known. Therefore, it is manifest that the use of “matter” to signify prime matter is less known to us than other uses. It is also true in this case that prime matter is less knowable by nature, because it lacks act, which is what gives things intelligibility.

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1. Physics, 191a 10-12 (Bk. 1, Part 7)

Faith in a mysterious, incomprehensible God seems to imply a contradiction. Faith demands that we declare Him certainly to exist, even to exist in a certain way. Mystery seems to silence any talk about Him at all. To know things about God, the believer may object, is to predicate things about Him; therefore, our ideas, abstracted from created things, must be applicable to God. Consequently, there is a likeness between God and creatures, which seems abhorrent to the utter transcendence of God. Rather, he would argue, we must believe in certain things about God, without knowing them. For, “we walk by faith, and not by sight.”¹ If knowledge of God is repugnant to the believer, however, utter ignorance of God seems to devoid faith of any content. One could say along with Cleanthes:

But if our ideas, so far as they go, be not just and adequate, and correspondent to his real nature, I know not what there is in this subject worth insisting on. Is the name, without any meaning, of such mighty importance?²

Pious belief in a God beyond the grasp of any finite intellect and desire to preach meaningful truths about Him seem to be at an impasse. To unravel this paradox, to justify the testimony of faith and the science of theology, it is necessary to understand more deeply the character of our knowledge of God. Rather than destroying God’s inscrutability, formal theology deepens His mystery by directing the mind toward what is beyond its comprehension.³

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1. 2 Cor. 5:7
2. Hume, Dialogues Concerning Natural Religion, Part IV, 158
3. Although I will use only Questions 1-12 of the Summa Theologica (S.T.), which concern knowledge of God that can be grasped by unaided human reason, the thesis still applies to knowledge of God had by faith through Revelation. For, even revealed truths are understood through words, whose concepts are abstracted from created things. Therefore, even knowledge by Revelation does not attain to the essence of God and does not oppose His mystery.