Know ye therefore ... - Learn from this case. It is an inference which follows, that all they who believe are the children of Abraham.
They which are of faith - Who believe, and who are justified in this manner.
Are the children of Abraham - Abraham was the “father of the faithful.” The most remarkable trait in his character was his unwavering confidence in God. They who evinced the same trait, therefore were worthy to be called his children. They would be justified in the same way, and in the same manner meet the approbation of God. It is implied here, that it was sufficient for salvation to have a character which would render it proper to say that we are the children of Abraham. If we are like him, if we evince the same spirit and character, we may be sure of salvation.