'Offspring' in the Bible

Now the promises [in the covenants] were decreed to Abraham and to his seed. God does not say, “And to seeds (descendants, heirs),” as if [referring] to many [persons], but as to one, “And to your Seed,” who is [none other than] Christ.

And if you belong to Christ [if you are in Him], then you are Abraham’s descendants, and [spiritual] heirs according to [God’s] promise.