26 Jesus the Son of Nun, the successor of Moses, was amazed; and came to him and said, “Have you heard that Eldad and Modad are prophesying? They were called, and they came not; my lord Moses, forbid them.” “I cannot forbid them,” he says, “for this grace is from Heaven; nay, so far am I from forbidding them, that I myself am thankful for it. I think not, however, that you have said this in envy; art thou jealous for my sake, because that they prophesy, and you prophesy not yet?
Wait for the proper season; and oh that all the Lord's people may be prophets, whenever the Lord shall give His Spirit upon them!” saying this also prophetically, whenever the Lord shall give; “For as yet then He has not given it; so you have it not yet.”— Had not then Abraham this, and Isaac, and Jacob, and Joseph? And they of old, had they it not? Nay, but the words, “whenever the Lord shall give” evidently mean “give it upon all; as yet indeed the grace is partial, then it shall be given lavishly.”
And he secretly alluded to what was to happen among us on the day of Pentecost; for He Himself came down among us. He had however also come down upon many before. For it is written, And Jesus the son of Nun was filled with a spirit of wisdom; for Moses had laid his hands upon him. You see the figure everywhere the same in the Old and New Testament—in the days of Moses, the Spirit was given by laying on of hands; and by laying on of hands Peter also gives the Spirit. And on you also, who art about to be baptized, shall His grace come; yet in what manner I say not, for I will not anticipate the proper season.
Source: Catechetical Lectures (New Advent)