Three times thou shalt keep a feast unto me in the year - The three feasts here referred to were,

1. The feast of the Passover;

2. The feast of Pentecost;

3. The feast of Tabernacles.

1. The feast of the Passover was celebrated to keep in remembrance the wonderful deliverance of the Hebrews from Egypt.

2. The feast of Pentecost, called also the feast of harvest and the feast of weeks, Exodus 34:22, was celebrated fifty days after the Passover to commemorate the giving of the law on Mount Sinai, which took place fifty days after, and hence called by the Greeks Pentecost.

3. The feast of Tabernacles, called also the feast of the ingathering, was celebrated about the 15th of the month Tisri to commemorate the Israelites' dwelling in tents for forty years, during their stay in the wilderness. See on Leviticus 23 (note).

"God, out of his great wisdom," says Calmet, "appointed several festivals among the Jews for many reasons:

1. To perpetuate the memory of those great events, and the wonders he had wrought for the people; for example, the Sabbath brought to remembrance the creation of the world; the Passover, the departure out of Egypt; the Pentecost, the giving of the law; the feast of Tabernacles, the sojourning of their fathers in the wilderness, etc.

2. To keep them faithful to their religion by appropriate ceremonies, and the splendor of Divine service.

3. To procure them lawful pleasures, and necessary rest.

4. To give them instruction; for in their religious assemblies the law of God was always read and explained.

5. To consolidate their social union, by renewing the acquaintance of their tribes and families; for on these occasions they come together from different parts of the land to the holy city."

Besides the feasts mentioned above, the Jews had,

continued...

Exodus 34:22 And you shall observe the feast of weeks, of the first fruits of wheat harvest, and the feast of ingathering at the year's end.

Leviticus 23:5,16,34 In the fourteenth day of the first month at even is the LORD's passover...

Deuteronomy 16:16 Three times in a year shall all your males appear before the LORD your God in the place which he shall choose...

The Wonderful.
Isaiah ix:6. HIS name shall be called "Wonderful" (Isaiah ix:6). And long before Isaiah had uttered this divine prediction the angel of the Lord had announced his name to be Wonderful. As such He appeared to Manoah. And Manoah said unto the angel of Jehovah, What is thy name, that when thy sayings come to pass we may do thee honor. And the angel of Jehovah said unto Him "why askest thou thus after my name, seeing it is Wonderful" (margin, Judges xiii:17-18). This angel of Jehovah, the Person who …
Arno Gaebelein—The Lord of Glory

The Blessing of Jacob Upon Judah. (Gen. Xlix. 8-10. )
Ver. 8. "Judah, thou, thy brethren shall praise thee; thy hand shall be on the neck of thine enemies; before thee shall bow down the sons of thy father. Ver. 9. A lion's whelp is Judah; from the prey, my son, thou goest up; he stoopeth down, he coucheth as a lion, and as a full-grown lion, who shall rouse him up? Ver. 10. The sceptre shall not depart from Judah, nor lawgiver from between his feet, until Shiloh come, and unto Him the people shall adhere." Thus does dying Jacob, in announcing …
Ernst Wilhelm Hengstenberg—Christology of the Old Testament

In the Temple at the Feast of Tabernacles.
(October, a.d. 29.) ^D John VII. 11-52. ^d 11 The Jews therefore sought him at the feast, and said, Where is he? [It was now eighteen months since Jesus had visited Jerusalem, at which time he had healed the impotent man at Bethesda. His fame and prolonged obscurity made his enemies anxious for him to again expose himself in their midst. John here used the word "Jews" as a designation for the Jerusalemites, who, as enemies of Christ, were to be distinguished from the multitudes who were in doubt …
J. W. McGarvey—The Four-Fold Gospel