Barnes' Notes on the Whole Bible

literally: “Beware that there be not in thy heart a word which is worthlessness” (compare Deuteronomy 13:13 note).

Thou shalt furnish him liberally - The verb in the Hebrew is remarkable. It means “thou shalt lay on his neck,” “adorn his neck with thy gifts.”

He hath been worth a double hired servant to thee, in serving thee six years - “i. e.” such a servant has earned twice as much as a common hired laborer would have done in the same time.

Compare Exodus 13:11 ff. The directions of the preceding legislation (see Numbers 18:15 ff) are here assumed, with the injunction added, that the animals thus set apart to God Deuteronomy 15:19 were not to be used by their owners for their earthly purposes. It is further allowed that firstborn animals which had a blemish should be regarded as exceptions, and instead of being given to God might be used as food Deuteronomy 15:21-22. The application of the firstborn of cattle is here directed as in Deuteronomy 12:6, Deuteronomy 12:17; Deuteronomy 14:23 : they are to be consumed in the sacred Feasts at the sanctuary.