23 Already on a former occasion I have spoken of these ascending and descending angels; but lest you should have forgotten, I shall speak of the latter briefly by way of recalling it to your recollection. I should use more words if I were introducing, not recalling the subject. Jacob saw a ladder in a dream; and on a ladder he saw angels ascending and descending: and he anointed the stone which he had placed at his head. You have heard that the Messias is Christ; you have heard that Christ is the Anointed.
For Jacob did not place the stone, the anointed stone, that he might come and adore it: otherwise that would have been idolatry, not a pointing out of Christ. What was done was a pointing out of Christ, so far as it behooved such a pointing out to be made, and it was Christ that was pointed out. A stone was anointed, but not for an idol. A stone anointed; why a stone? “Behold, I lay in Zion a stone, elect, precious: and he that believes in Him shall not be confounded.” Why anointed?
Because Christus comes from chrisma. But what saw he then on the ladder? Ascending and descending angels. So it is the Church, brethren: the angels of God are good preachers, preaching Christ; this is the meaning of, “they ascend and descend upon the Son of man.” How do they ascend, and how do they descend? In one case we have an example; listen to the Apostle Paul. What we find in him, let us believe regarding the other preachers of the truth. Behold Paul ascending: “I know a man in Christ fourteen years ago was caught up into the third heaven (whether in the body, or whether out of the body, I cannot tell: God knows), and that he heard unspeakable words, which it is not lawful for a man to utter.” You have heard him ascending, hear him descending: “I could not speak unto you as unto spiritual, but as unto carnal; as babes in Christ I have fed you with milk, not with meat.” Behold he descended who had ascended.
Ask whether he ascended to the third heaven. Ask whether he descended to give milk to babes. Hear that he descended: “I became a babe in the midst of you, even as a nurse cherishes her children.” For we see both nurses and mothers descend to babes, and although they be able to speak Latin, they shorten the words, shake their tongues in a certain manner, in order to frame childish endearments from a methodical language; because if they speak according to rule, the infant does not understand nor profit.
And if there be a father well skilled in speaking, and such an orator that the forum resounds with his eloquence, and the judgment-seats shake, if he have a little son, on his return home he puts aside the forensic eloquence to which he had ascended, and in child's language descends to his little one. Hear in one place the apostle himself ascending and descending in the same sentence: “For whether,” says he,“we be beside ourselves, it is to God; or whether we be sober, it is for your cause.” What is “we are beside ourselves”?
That we see those things which it is not lawful for a man to speak. What is “we are sober for your cause? Have I judged myself to know anything among you, save Jesus Christ and Him crucified?” If the Lord Himself ascended and descended, it is evident that His preachers ascend by imitation, descend by preaching.
Source: Tractates on the Gospel of John (New Advent)