One question that needs to be asked is what kind of veneration are we offering to the cross during the Good Friday service? Another is whether that kind of veneration can belong to the cross simply or if it necessitates the image of Christ Crucified?
The Church has long tradition of very clear language that only God is to be worshipped with the latria." In fact, the Catholic Church distinguishes between three forms of veneration: latria, hyperdulia, and dulia. St. Thomas says:
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Reverence is due to God on account of His excellence, which is communicated to certain creatures not in equal measure, but according to a measure of proportion; and so the reverence which we pay to God, and which belongs to latria, differs from the reverence which we pay to certain excellent creatures; this belongs to dulia, and we shall speak of it further on (103).In Q. 103, St. Thomas continues:
Wherefore dulia, which pays due service to a human lord, is a distinct virtue from latria, which pays due service to the lordship of God. It is, moreover, a species of observance, because by observance we honor all those who excel in dignity, while dulia properly speaking is the reverence of servants for their master, dulia being the Greek for servitude.Now, hyperdulia is reserved for Mary Mother of God. It is nothing more than the highest reverence to any creature. Nevertheless, even hyperdulia falls short of the homage paid to God. Naturally, the question arises in the Summa Theologica, whether we ought to worship Christ's humanity with the adoration of latria, for Christ's body is a created thing. The entirety of his humanity is creaturely. And yet His humanity is united to the Divine Nature by His Person. The cause of the honor due to Christ, in His humanity, is the dignity of His Person, and therefore, it follows that Christ's humanity is worshipped with the adoration of latria (III, Q. 25, a. 1-2).
The veneration of Christ's humanity can, however, be thought of in more than one way. In as much as it is His humanity, it is adored with latria. If his humanity is venerated on account of its perfection by the gifts of grace, it is not the Person, and therefore not the Godhead, that is being paid homage, but the perfection of humanity, which is nevertheless praiseworthy. On this veneration of His perfect humanity, St. Thomas says:
And then thus understood as distinct from the Word of God, it should be adored with the adoration of "dulia"; not any kind of "dulia," such as is given to other creatures, but with a certain higher adoration, which is called "hyperdulia"... Because the adoration of "latria" is not given to Christ's humanity in respect of itself; but in respect of the Godhead to which it is united, by reason of which Christ is not less than the Father (III, Q. 25, a. 2).Now, if Christ's humanity is worshipped with the adoration of latria by virtue of its unity with the Godhead, then what about an image of Christ? Certainly the image is not united to the Godhead, and therefore, in itself is not deserving of latria. There is, however, as St. Thomas puts it, a twofold movement of the mind towards and image. There first, of course, toward the image as a thing. If a statue, the mind moves toward it first as a thing of plaster or stone. There is another movement that the mind makes towards and image, namely insofar as it is the image of something else. According to this second movement of the mind, the movement does not terminate in the stone and plaster of the statue, but rather, it terminates in the thing imaged.
In as much as it is an image, reverence is due to it. The reverence shown to it as image terminates not in it as a thing of plaster or stone, but rather in the person imaged. St. Thomas says:
It follow [sic] therefore that reverence should be shown to it, in so far only as it is an image. Consequently the same reverence should be shown to Christ's image as to Christ Himself. Since, therefore, Christ is adored with the adoration of "latria," it follows that His image should be adored with the adoration of "latria" (III, Q. 25, a. 3).This then, brings us to the matter of the Cross of Christ, which we venerate on Good Friday. St. Thomas is clear that reverence of any kind is due to persons and not to things. The cross is simply not a person, and so it would seem that no reverence whatsoever is due to it. This, however, is not the conclusion to which St. Thomas comes. By the subtlety of his intellect St. Thomas is able to find the distinction that we seem to fail to grasp on our own. Things are reverenced by reason a rational nature in two ways (emphasis mine):
First, inasmuch as it represents a rational nature: secondly, inasmuch as it is united to it in any way whatsoever. In the first way men are wont to venerate the king's image; in the second way, his robe. And both are venerated by men with the same veneration as they show to the king.In an age where monarchs are few and far between, let alone our chance encounters with them, it becomes difficult to grasp this. If we look at our own personal relations maybe we can come to a similar conclusion. The person who carries a picture of his family or spouse and kisses it from time to time, is no different than the person who venerates the kings image. The young man who has received his dead father's pocket watch and carries it with him everywhere, is no different than the one who reverences the king's robe. The same care that he shows to that watch is a love that terminates in his father who he associates so closely with it.
So, as concerns any relic of the True Cross, St. Thomas says:
If, therefore, we speak of the cross itself on which Christ was crucified, it is to be venerated by us in both ways--namely, in one way in so far as it represents to us the figure of Christ extended thereon; in the other way, from its contact with the limbs of Christ, and from its being saturated with His blood. Wherefore in each way it is worshiped with the same adoration as Christ, viz. the adoration of "latria." And for this reason also we speak to the cross and pray to it, as to the Crucified Himself.This is why Fr. Z can say, "If there is no relic of the True Cross available for veneration, then the Crucifix should be used." There is a greater tradition of veneration of the True Cross and to the Crucifix as a substitute, but St. Thomas does not leave it at that. He continues:
But if we speak of the effigy of Christ's cross in any other material whatever--for instance, in stone or wood, silver or gold--thus we venerate the cross merely as Christ's image, which we worship with the adoration of "latria," as stated above (Article 3).So, whether it be a relic of the True Cross, a crucifix, or a bare cross, the adoration of latria is offered. To the True Cross latria is offered in a twofold way, by representation and by way of it being united to Christ by contact. Both the crucifix and the bare cross are only worshipped with the adoration of latria in as much as they are images of Christ.
Since there is no difference in the worship offered, it would seem that the best way to answer this question would be to ask whether in the rite of the Veneration of the Cross, we are called to venerate Christ or His Cross. It seems clear in the rite, that the veneration is of the cross itself, as the means by which our salvation is effected, is what we venerate in as much as it is associated with Christ. Therefore, since there is no image of Christ Crucified without a cross, it would seem appropriate to venerate either the a crucifix or, out of necessity, a bare cross will suffice. By kissing the cross or the feet of Christ, the worship offered is the same—latria—and to terminates in the same Person imaged—the Word of God, Christ.