Moses had finished what he had to say about provisions for the needy (the Levites, aliens, orphans, widows, the poor, and slaves; Deuteronomy 14:22 to Deuteronomy 15:18). Here his thoughts turned back to the subject of the first-born of animals that he mentioned previously when he addressed the sacrificial meals ( Deuteronomy 12:6; Deuteronomy 12:17; Deuteronomy 14:23). [source][source][source]
The Israelites were not to use their first-born male animals for personal gain but were to offer them to God as sacrifices. The Law taught them to regard them as God"s possessions (cf. Exodus 13:2; Exodus 13:12). They could eat defective first-born animals at their homes rather than offering them at the tabernacle and eating them there. In all cases they were to set aside first-born oxen and sheep for God as sacrifices because God had blessed the herd or flock with fertility. The Israelites were to offer God as near a perfect specimen as possible. This taught them that God deserves the very best, which would have cost them the most. [1][source]
As Christians we too should acknowledge God"s goodness if He increases our possessions. Our sacrifices need not be the first-born animals of our herds or flocks, but they might be verbal thanksgiving ( Hebrews 13:15), our labor, our money, indeed our very lives ( Romans 12:1-2). [source][source][source]