Joel 2:29

29. And also--"And even." The very slaves by becoming the Lord's servants are His freemen (1Co 7:22; Ga 3:28; Col 3:11; Phm 16). Therefore, in Ac 2:18 it is quoted, "My servants" and "My handmaidens"; as it is only by becoming the Lord's servants they are spiritually free, and partake of the same spirit as the other members of the Church.

Robert Jamieson, A. R. Fausset & David Brown, 1871 · public domain

Verse 29 And also upon the servants and upon the handmaids - The gifts of teaching and instructing men shall not be restricted to any one class or order of people. He shall call and qualify the men of his own choice; and shall take such out of all ranks, orders, degrees, and offices in society. And he will pour out his Spirit upon them; and they shall be endowed with all the gifts and graces necessary to convert sinners, and build up the Church of Christ on its most holy faith. And this God has done, and is still doing. He left the line of Aaron, and took his apostles indiscriminately from any tribe. He passed by the regular order of the priesthood, and the public schools of the most celebrated doctors, and took his evangelists from among fishermen, tent-makers, and even the Roman tax-gatherers. And he, lastly, passed by the Jewish tribes, and took the Gentile converts, and made them preachers of righteousness to the inhabitants of the whole earth. The same practice he continues to the present day; yet he did not then pass by a man brought up at the feet of Gamaliel, no more than he would now a man brought up in a celebrated seminary of learning. He is ever free to use his own gifts, in his own way; and when learning is sanctified, by being devoted to the service of God, and the possessor is humble and pious, and has those natural gifts necessary for a public teacher, perhaps we might safely say, God would in many cases prefer such: but he will have others, as intimated in the prophecy, that we may see the conversion of men is not by human might, nor power, but by the Spirit of the Lord of hosts. The learned man can do nothing without his Spirit; the unlearned must have his gifts and graces, without which both their labors would be unprofitable; and thus the excellency of the power is of God, and no flesh can glory in his presence. See my sermon on this passage.

Adam Clarke, 1831 · public domain