Moses had finished what he had to say about provisions for the needy (the Levites, the alien, orphans, widows, the poor, and slaves; 14:22-15:18). Here his thoughts turned back to the subject of the first-born of animals that he mentioned previously when he addressed the sacrificial meals (12:6, 17; 14:23).
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. Exod. 13:2, 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.182
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 (Heb. 13:15), our own labor, our money, indeed our very lives (Rom. 12:1-2).