Albert Barnes Commentary Galatians 4:7

"So that thou art no longer a bondservant, but a son; and if a son, then an heir through God." — Galatians 4:7 (ASV)

Therefore. In consequence of this privilege of addressing God as your Father.

Thou art no more. You who are Christians.

A servant. In the servitude of sin; or treated as a servant by being bound under the oppressive rites and ceremonies of the law. Compare Galatians 4:3.

But a son. A child of God, adopted into his family, and to be treated as a son.

And if a son, etc. Entitled to all the privileges of a son, and of course to be regarded as an heir through the Redeemer, and with Him. See Romans 8:17 for an explanation of the sentiment expressed here.