The apostle deals plainly with those who urged the law of Moses together with the gospel of Christ, and endeavoured to bring believers under its bondage. They could not fully understand the meaning of the law as given by Moses. And as that was a dispensation of darkness, so of bondage; they were tied to many burdensome rites and observances, by which they were taught and kept subject like a child under tutors and governors. We learn the happier state of Christians under the gospel dispensation. From these verses see the wonders of Divine love and mercy; particularly of God the Father, in sending his Son into the world to redeem and save us; of the Son of God, in submitting so low, and suffering so much for us; and of the Holy Spirit, in condescending to dwell in the hearts of believers, for such gracious purposes.

Matthew Henry, Commentary on Galatians 4:1-7