In the fourth year, the Hebrews may still not eat the fruit. The fruit belongs to the Lord as an offering of praise. The phrase offering of praise
is only used on one other occasion in the Old Testament (Judges 9:27). The fourth year is understood to be one of celebration and devotion because God has given good gifts to his people.
24 And in the fourth year all its fruit shall be holy, an offering of praise to the LORD.