John Calvin Commentary Galatians 4:31

"Wherefore, brethren, we are not children of a handmaid, but of the freewoman." — Galatians 4:31 (ASV)

So then, brethren. He now exhorts the Galatians to prefer the condition of the children of Sarah to that of the children of Hagar; and having reminded them that, by the grace of Christ, they were born to freedom, he desires them to continue in the same condition. If we call the Papists Ishmaelites and Hagarites, and boast that we are the lawful children, they will smile at us; but if the two subjects in dispute are fairly compared, the most ignorant person will be at no loss to decide.