Firstborn Animals Already Belong to YHWH
A worshiper cannot dramatically “give” God a firstborn animal as a new vow because it already belongs to God under the Exodus firstborn law.
Where this fits in the story: Exodus 13:1–16 — Very Strong/Certain: firstborn belong to YHWH because of the exodus/Passover deliverance.
Where Scripture takes it next: NT “firstborn” Christology is important but arises through multiple distinct firstborn traditions; no NT writer cites Leviticus 27:26–27 as the messianic prooftext.