Many members of the Galatian church, and many professing Christians since, have supposed that sinners are saved by their own best efforts, by keeping the law of Moses as promulgated in the Sinai covenant.

As Paul insists in Galatians 3 and 4, this is a fatal error, because it undermines the gospel of God’s free grace.

David Murray shows how the Sinai covenant is, in face, ‘a revelation of Jesus and his gracious salvation.’  Like this:-

1. ‘The Sinai covenant painted pictures of grace.  The moral law of Exodus 20 was preceded by the grace of the Passover lamb, concluded by the covenant ratification sacrifices, and followed by the gracious provision and acceptance of the sacrificial lambs in the ceremonial law…’
2. ‘The Sinai covenant is set in the context of grace.  Exodus 19:4-5 sets forth all God had done in delivering Israel from Egypt as the basis for the divine “therefore obey”…’
3. ‘The Sinai covenant points to our need of grace.’  It shows our desperate need and leads us, as faithful teacher, to the Saviour, so that we might be justified by faith (Gal 3:25f).
4. ‘The Sinai covenant shows how we are to respond to grace.’  God’s gracious redemption, which has brought us into a gracious relationship with him, is followed by a divine ‘therefore obey’, Ex 19:5; 20:34.  Our obedience to God’s law flows out of gratitude for his grace.

Jesus on Every Page, Thomas Nelson, pp 29-32.