וּבַשָּׁנָה֙ הָרְבִיעִ֔ת יִהְיֶ֖ה כָּל־פִּרְי֑וֹ קֹ֥דֶשׁ הִלּוּלִ֖ים לַיהוָֽה׃
И в четвертый год все плоды его будут святы, чтобы воздавать хвалу Господу.
Rashi
יהיה כל פריו קדש [BUT IN THE FOURTH YEAR] THE FRUIT THEREOF SHALL BE HOLY, in the same way as the "second tithe" with reference to which, too, it is stated (Leviticus 27:30) "And all the tithe of the land… [belongeth to the Lord]; it is holy (קדש) unto the Lord". Now what is the law regarding the “second tithe"? It must not be eaten outside the walls of Jerusalem except after redemption! The same is the case with this (the fruit in the fourth year). And this very thing הלולים לה׳, is A PRAISE OF THE LORD, for he takes it there (to Jerusalem) to praise and to laud God in Heaven, as he does with the second tithe (cf. Berakhot 35a).
Ibn Ezra
praisegiving In order to praise God. This fruit must be eaten by the kohanim.
Rashbam
קדש הלולים. Possessing a degree of sanctity similar to that of the second tithe which may only be consumed in Jerusalem. The objective of the legislation is to praise the Creator thanks to whose generosity the farmer enjoys the abundance of these fruit of the soil tilled by him. We are to learn to revere G’d by means of such commandments (Deut. 14,23).