Firstborn sons and firstborn donkeys belonged to Yahweh, but Yahweh did not want them sacrificed to him. Instead, the Israelites were to sacrifice a lamb in their place. This allowed the Israelites to redeem or buy back the donkeys and sons from Yahweh.
God speaks of the offering as if the person was to carry it in his hands. Alternate translation: "No one may come to me without an offering" or "Everyone who comes to me must bring me an offering" (See: [[rc://en/ta/man/jit/figs-metonymy]])