25 This Spirit descended upon the seventy Elders in the days of Moses. (Now let not the length of the discourse, beloved, produce weariness in you: but may He the very subject of our discourse grant strength to every one, both to us who speak, and to you who listen!) This Spirit, as I was saying, came down upon the seventy Elders in the time of Moses; and this I say to you, that I may now prove, that He knows all things, and works as He will. The seventy Elders were chosen; And the Lord came down in a cloud, and took of the Spirit that was upon Moses, and put it upon the seventy Elders; not that the Spirit was divided, but that His grace was distributed in proportion to the vessels, and the capacity of the recipients. Now there were present sixty and eight, and they prophesied; but Eldad and Modad were not present: therefore that it might be shown that it was not Moses who bestowed the gift, but the Spirit who wrought, Eldad and Modad, who though called, had not as yet presented themselves, did also prophesy.
Source: Catechetical Lectures (New Advent)