In Gen. 12:3, the LORD promised Abram in him or through him (i.e., Abram) all the families of the earth will be blessed.
A Gentile in the present age who believes in Christ belongs to Him and is “in Christ” therefore considered as a seed of Abraham. This blessing (promise of the Spirit) to the Gentiles comes under the promise to Abram to bless all the families of the earth (Gen. 12:3; Gal. 3:6-9) ... the third (not the second) promise to Abram.