Contradiction with Numbers 18:15
Unlike Exodus 13:12, Numbers 18:15 states that the firstborn of both humans and animals are to be redeemed, rather than set apart for the Lord.
Numbers 18:15: Every thing that openeth the matrix in all flesh, which they bring unto the LORD, [whether it be] of men or beasts, shall be thine: nevertheless the firstborn of man shalt thou surely redeem, and the firstling of unclean beasts shalt thou redeem.
Contradiction with Leviticus 27:26
This verse implies that the firstborn does not need to be dedicated because it already belongs to the Lord, which contradicts the act of setting apart as described in Exodus 13:12.
Leviticus 27:26: Only the firstling of the beasts, which should be the LORD'S firstling, no man shall sanctify it; whether [it be] ox, or sheep: it [is] the LORD'S. [firstling of: Heb. firstborn, etc]
Contradiction with Deuteronomy 15:19
This verse instructs not to do any work with the firstborn, implying a continual domestic use, contrary to the separation for the Lord in Exodus 13:12.
Deuteronomy 15:19: All the firstling males that come of thy herd and of thy flock thou shalt sanctify unto the LORD thy God: thou shalt do no work with the firstling of thy bullock, nor shear the firstling of thy sheep.
Paradox #1
Exodus 13:12 may seem inconsistent with verses that speak about God's ownership of everything and not requiring offerings from people, like Psalm 50:10-12, where God says everything already belongs to Him. This can raise questions about why specific offerings are needed.
Paradox #2
The potential doctrinal issue with Exodus 13:12 is the requirement to dedicate every firstborn to God, which could clash with later practices or beliefs about personal ownership and inheritance rights. Some might also see a conflict with the concept of animal sacrifices being replaced by Jesus' sacrifice in the New Testament. Overall, interpretations and beliefs can vary among different religious groups, so this could be seen differently depending on the doctrinal perspective.