Theophylact of Ohrid

He said "of His own will" because there are people who, by the instigation of the devil, reason that the world came together as if by chance. Above he said: "with whom there is no variation," and thereby showed that the Divinity is unchangeable; now he adds: "of His own will He brought us forth." If we came into being, then it is evident that we are not unchangeable, for is it possible that what came from non-being into being through change should be unchangeable? …

Commentary on James ↗

Bede

That we might be a kind of firstfruits of His creatures. Lest we imagine that by saying, "He begot us," we become what He is, this demonstrates that a certain preeminence is granted to us in creation by this adoption. Indeed, some have translated the verses as follows: "Of His own will He begot us with the word of truth, that we should be a kind of firstfruits of His creatures." That is, that we should be better than the other creatures we see. …

Commentary on the Catholic Epistles ↗

Bonaventure

He is called the Father of the age to come, for He Himself is the Principle of those influences by which we will live in the future. As James writes: "Every good gift and every perfect gift is from above, coming down from the Father of Lights." And later: "Of His own will He has begotten us by the word of truth, that we might be, as it were, the first-fruits of His creatures." We are now the beginning of creatures, but then we shall be creatures in full.

Collations on the Hexaemeron, Collation 3 ↗