Albert Barnes Commentary Exodus 23:14-17

"Three times thou shalt keep a feast unto me in the year. The feast of unleavened bread shalt thou keep: seven days thou shalt eat unleavened bread, as I commanded thee, at the time appointed in the month Abib (for in it thou camest out from Egypt); and none shall appear before me empty: and the feast of harvest, the first-fruits of thy labors, which thou sowest in the field: and the feast of ingathering, at the end of the year, when thou gatherest in thy labors out of the field. Three times in the year all thy males shall appear before the Lord Jehovah." — Exodus 23:14-17 (ASV)

This is the first mention of the three great Yearly Festivals. The Feast of Unleavened Bread, in its connection with the Paschal Lamb, is spoken of in Exodus 12 and Exodus 13; but the two others are first named here. All three are spoken of as if they were familiarly known to the people. The points that are especially commanded are that every male Israelite should attend them at the sanctuary , and that he should take with him an offering for Yahweh, presenting himself before his King with his tribute in his hand. That this condition belonged to all the feasts, though it is stated here only in regard to the Passover, cannot be doubted. See Deuteronomy 16:16. (Exodus 23:15–16)

On the Feast of Unleavened Bread, or the Passover, see Exodus 12:1-20, Exodus 12:43–50, Exodus 13:3–16, Exodus 34:18–20, and Leviticus 23:4-14; on the Feast of the Firstfruits of Harvest (also called the Feast of Weeks and the Feast of Pentecost), see Exodus 34:22 and Leviticus 23:15-21; on the Feast of Ingathering (also called the Feast of Tabernacles), see Leviticus 23:34-36 and Leviticus 23:39-43. (Exodus 23:16)

In the end of the year. Compare to Exodus 34:22. The year spoken of here must have been the civil or agrarian year, which began after harvest, when the ground was prepared for sowing. Compare to Leviticus 23:39 and Deuteronomy 16:13-15. The sacred year began in spring, with the month Abib, or Nisan. See the note on Exodus 12:2 and Leviticus 25:9.

When you have gathered. Rather, "when you gather in."