God spoke to Moses with a command that sounds absolute: "Sanctify unto Me every first-born" (Exodus 13:1-2). Every first-born — of humans, of animals, of everything that opens the womb — belongs to God. The Mekhilta identifies this as an example of one of the thirteen interpretive principles by which the Torah is expounded: a generic statement that requires a specific one to define it, and a specific statement that requires a generic one to expand it.
"Sanctify unto Me every first-born" is the generic statement. Standing alone, it is almost impossibly broad. Every first-born of every species? First-born males and females alike? First-born of Jews and non-Jews? The command needs boundaries.
The specific statements that follow — detailing which first-born animals are sanctified, how the first-born of a donkey is redeemed, how the first-born son is redeemed through the priests — provide those boundaries. The general principle establishes that first-born status carries holiness. The specific laws explain exactly how that holiness is expressed in practice.
This hermeneutical principle (known as klal u-frat, "the general and the particular") was one of the essential tools the rabbis used to derive law from Scripture. The Torah frequently pairs sweeping declarations with detailed instructions, and the interplay between the two generates the actual legal framework. Without the general statement, the specifics would seem arbitrary. Without the specifics, the general statement would be unworkable. Together, they form a complete system — exactly as the thirteen principles intend.