God made promises to Abraham (Gen.12:1-3, &17:7) & his’ Descendant/The Seed‘. Christ, the Messiah was coming from Abraham’s lineage, but some Jews stumbled on this (Isaiah 28:16, Rom. 9:33), they misinterpreted it & took it the blessings were just for all Abraham’s descendants in the flesh, Israelites. Sadly many Jews still believe that today!
In the Old Testament the Hebrew word H2233 Zera, = “seed” is a singular noun that can also mean offspring (collective). Many modern bibles translate or change the Hebrew word “seed” as “descendants,” “children,” (plural only), see Gen.17. The Hebrew text could have used a plural form, like the word ‘Generations’ (plural) in Hebrew is H1755= dore, or H6631=descendants, offspring, or the word ‘mishpachan’ H4940, etc, if wanted to make clear it was plural. This miss translation makes it difficult to understand, altering the scriptures & the doctrine. In Greek language there are distinct words for seed (spermati) & seeds (spermasin).