Theme: Jesus Christ brings God’s promised inheritance to all who believe; don’t go back to old covenant law

Isn’t seed normally plural?
The Hebrew word for seed is a collective singular. It can refer to many or to one (cf. Genesis 13:15; 17:8). Jesus is the representative offspring of Abraham (singular, 3:16), the fulfilment of the original redemptive promise given in Genesis 3:15. He is the only one who has the right to inheritance (life in God’s presence, 3:18). Those united to him by faith are also offspring of Abraham (collective, 3:29), sharing in the inheritance that he was won (3:26).

What does Paul mean when he says “an intermediary implies more than one, but God is one?”
This verse has prompted many different interpretations. Read in context, it compares the promises given to Abraham (3:18) with the law entrusted to Moses (3:19). Most likely, Paul draws attention to the fact that God spoke directly to Abraham (cf. Genesis 12, 15), whilst at Sinai the angels were also involved. Implicit in his argument is the idea that direct revelation is better than mediated revelation, and thus the Abrahamic covenant is superior to (and served by) Moses.