The Proper Order of Tithes and the Firstborn Given to God

"Your fullness and your tithe-offering" (Exodus 22:28). "Your fullness" refers to the first fruits, which are taken from the fullness of the produce. "Your tithe-offering" refers to the priestly portion (terumah), which is called "a tithe-offering." "You shall not delay." Do not delay a thing that is fitting to put first. This teaches that whoever puts the priestly portion before the first fruits, or the first tithe before the priestly portion, or the second tithe before the first, transgresses a negative commandment. Rather, he separates them in their order: first fruits, and after them the priestly portion, and after them the first tithe, and after it the second tithe. Rabbi Eliezer ben Yaakov says: "You shall not delay" means that you shall not delay them at the time of the threshing-floor from giving them to their owners [the priests and Levites]. "The firstborn of your sons you shall give to Me" (Exodus 22:28). One might think he must literally give them to Me. Scripture says, "And Moses gave the redemption money to Aaron and his sons" (Numbers 3:51). I know this only for that time; from where do I learn it for the generations? Scripture says, "by the mouth of the LORD, as the LORD commanded Moses" (Numbers 3:51). If so, why does it say "the firstborn of your sons you shall give to Me"? As long as you give him according to His commandment, I credit it to you as though you had given him to Me; and if not, I credit it to you as though you had robbed Me.