5 And yet let no one say that such things had no good signification because they were done by the bad, that is to say, not by those who followed Christ, but by those who perse cuted Him. For what could we have to say of the cross itself, which every one knows was in like manner made and fastened to Christ by enemies and sinners? And yet it is to it we may rightly understand the words of the apostle to be applicable, “what is the breadth, and the length, and the height, and the depth.” For its breadth lies in the transverse beam, on which the hands of the Crucified are extended; and signifies good works in all the breadth of love: its length extends from the transverse beam to the ground, and is that whereto the back and feet are affixed; and signifies perseverance through the whole length of time to the end: its height is in the summit, which rises upwards above the transverse beam; and signifies the supernal goal, to which all works have reference, since all things that are done well and perseveringly, in respect of their breadth and length, are to be done also with due regard to the exalted character of the divine rewards: its depth is found in the part that is fixed into the ground; for there it is both concealed and invisible, and yet from thence spring up all those parts that are outstanding and evident to the senses; just as all that is good in us proceeds from the depths of the grace of God, which is beyond the reach of human comprehension and judgment. But even though the cross of Christ signified no more than what was said by the apostle, “And they who are Jesus Christ's have crucified the flesh with the passions and lusts,” how great a good it is! And yet it does not this, unless the good spirit be lusting against the flesh, seeing that it was the opposing, or, in other words, the evil spirit that constructed the cross of Christ. And lastly, as every one knows, what else is the sign of Christ but the cross of Christ? For unless that sign be applied, whether it be to the foreheads of believers, or to the very water out of which they are regenerated, or to the oil with which they receive the anointing chrism, or to the sacrifice that nourishes them, none of them is properly administered. How then can it be that no good is signified by that which is done by the wicked, when by the cross of Christ, which the wicked made, every good thing is sealed to us in the celebration of His sacraments? But here we stop; and what follows we shall consider at another time in the course of dissertation, as God shall grant us assistance.
Source: Tractates on the Gospel of John (New Advent)