Charles Ellicott Commentary Deuteronomy 12:26

"Only thy holy things which thou hast, and thy vows, thou shalt take, and go unto the place which Jehovah shall choose:" — Deuteronomy 12:26 (ASV)

Only your holy things ... and your vows. —The holy things probably mean the firstlings, which were necessarily holy, and must be made burnt offerings (Deuteronomy 12:6). The second tithe was also considered holy. The first tithe, or ordinary provision for the Levites (see Numbers 18), was not considered holy. The vows might be either burnt offerings or peace offerings.