“The law was given to Israel not that they might be redeemed, but because they had been redeemed. The nation had been brought out of Egypt by the power of God under the blood of the slain lamb, itself the symbol and token of His grace. The law was added at Sinai as the necessary standard of life for a ransomed people, a people who now belonged to the Lord. It began with a declaration of their redemption; ‘I am the Lord thy God who brought thee out of the land of Egypt, out of the house of bondage’ (Ex. 20:2). It rested on the basis of grace, and it embodied the principle that redemption implied a conformity to God’s moral order. In other words, the very grace that redeemed Israel carried with it the necessity of revealing the law to Israel. The law was given that they might walk worthy of the relation in which they now stood to God, worthy of a salvation which was already theirs. The covenant of the law did not supersede the covenant of promise, but set forth the kind of life which those who were redeemed by the covenant of promise were expected to live.
The law was not a covenant of works in the sense that Israel’s salvation depended upon obedience to it. The devout Israelite was saved by faith in the promise of God, which was now embodied in the tabernacle services. He looked forward through the sacrifices to a salvation which they foreshadowed, and by faith accepted it, as we look back to the Cross and by faith accept the salvation which has been accomplished. The Old Testament saints and the New Testament saints are both saved in the same way, and that is, by the grace of God through Jesus Christ alone.‘
from “The Law and the Saint” by Arthur. W. Pink, Studies in the Scriptures, Published from 1922 to 1952.