Skipping over the theological introduction, which doesn't seem to have much to do with his argument, here's what he says as to why Protestants object to Catholic practice on this score (see TF's post, linked above, for the Hodge quotes).
1. Because it supposes a class of beings who do not exist; that is, of canonized departed spirits. It is only those who, with the angels, have been officially declared by the Church, on account of their merits, to be now in heaven, who are regarded as intercessors.Well, right out of the starting gate Hodge gets it woefully wrong, and he exposes not just that he is wrong, but his complete ignorance of the Catholic view of the subject.
In the first place, he doesn't seem to have any idea what canonization means in the Catholic Church (with respect to the saints, not the canon of Scripture, which is a different subject).
The Catholic Church canonizes or beatifies only those whose lives have been marked by the exercise of heroic virtue, and only after this has been proved by common repute for sanctity and by conclusive arguments. The chief [thing] lies in the meaning of the term canonization, the Church seeing in the saints nothing more than friends and servants of God whose holy lives have made them worthy of His special love [Catholic Encyclopedia].But in particular, canonization has to do with identifying those who may be mentioned and invoked in the liturgy:
It must be obvious, however, that while private moral certainty of their sanctity and possession of heavenly glory may suffice for private veneration of the saints, it cannot suffice for public and common acts of that kind. No member of a social body may, independently of its authority, perform an act proper to that body [Catholic Encyclopedia article again].The Catholic Church doesn't create saints when it canonizes them; it simply recognizes that which already is the case. So it's a bizarre assertion on Hodge's part to object that prayers to saints are wrong "Because it supposes a class of beings who do not exist; that is, of canonized departed spirits." But the saints are departed spirits. And they have been canonized - that is, added to the rolls of those who may be publicly venerated in the liturgy. Hodge makes it sound like there is some bizarre ontological distinction ("class of beings") and that canonization has performed some constitutional change in them. But that's nearly unintelligible, and it has nothing to do with what Catholics mean by canonization.
Furthermore, it is not merely the saints to whom we may for intercession. This should be obvious from this fact: a typical means by which the Church identifies those who may be candidates for canonization is an allegedly miraculous answer to prayers offered to one who is not already identified as a saint (I say "allegedly" because such events are investigated before being accepted). The point, though, is that we seek their intercession just as we seek the intercession of our friends and family still living here on earth, only all the more so when we seek the intercession of the saints, because "the unceasing prayer of a just man is of great avail" (James 5:16). It is nothing but an a fortiori argument: if the prayers of a righteous man still living on earth are effective, how much more are the prayers of those in heaven going to be effective, whose righteousness has been confirmed by their being in God's presence! So then, Hodge gets it wrong when he says that only the canonized may be regarded as intercessors.
Hodge continues, by way of contradicting the straw man that he has just set up:
This, however, is an unauthorized assumption on the part of the Church. It has no prerogative to enable it thus to decide, and to enroll whom it will among glorified spirits.But the Church makes no such silly assumptions, doesn't claim such a prerogative, and doesn't pretend to enroll anyone as a "glorified spirit."
Moving on from this dreadful beginning, Hodge continues with his second point:
2. It leads to practical idolatry. Idolatry is the ascription of divine attributes to a creature. In the popular mind the saints, and especially the Virgin Mary, are regarded as omnipresent; able at all times and in all places, to hear the prayers addressed to them, and to relieve the wants of their worshippers.This is a standard and ridiculous canard. I know of no Catholics who worship the saints as gods. This is typical Protestant mind-reading to which I have objected before (and of course all Catholics object to it; there is nothing special about my complaint!).
But a second part of the objection is that the saints are asserted by Hodge to be unable to hear all the prayers addressed to them, by virtue of the fact that they are not God (and so, because we say that they do hear them, it is wrongly assumed as proven by Hodge that we treat them as deities). In response to this, I would point the reader at my patron's remarks on the subject here (ST Supp Q72 A1).
The Divine essence is a sufficient medium for knowing all things, and this is evident from the fact that God, by seeing His essence, sees all things. But it does not follow that whoever sees God's essence knows all things, but only those who comprehend the essence of God [Cf. I, 12, 7,8: even as the knowledge of a principle does not involve the knowledge of all that follows from that principle unless the whole virtue of the principle be comprehended. Wherefore, since the souls of the saints do not comprehend the Divine essence, it does not follow that they know all that can be known by the Divine essence--for which reason the lower angels are taught concerning certain matters by the higher angels, though they all see the essence of God; but each of the blessed must needs see in the Divine essence as many other things as the perfection of his happiness requires. For the perfection of a man's happiness requires him to have whatever he will, and to will nothing amiss: and each one wills with a right will, to know what concerns himself. Hence since no rectitude is lacking to the saints, they wish to know what concerns themselves, and consequently it follows that they know it in the Word. Now it pertains to their glory that they assist the needy for their salvation: for thus they become God's co-operators, "than which nothing is more Godlike," as Dionysius declares (Coel. Hier. iii). Wherefore it is evident that the saints are cognizant of such things as are required for this purpose; and so it is manifest that they know in the Word the vows, devotions, and prayers of those who have recourse to their assistance.In short: Hodge's objection here assumes that there is no change whatsoever in what may be known by those who are in heaven. It is an unwarranted assumption, and I think that St. Thomas sufficiently responds to it.
Now I've only gone through two of Hodge's arguments, and this is getting to be ridiculously long. We'll continue in a second post.