Here is a quick sweeping picture of the history of redemption.
God has revealed Himself in space-time history by becoming flesh in the Person of Jesus Christ. His purpose was to glorify Himself by redeeming sinful, fallen creatures from their bondage and captivity to sin and its deadly consequences. He did this by becoming our representative (Heb 2:17; 4:15), doing for us from our side what we were unable to do for ourselves. He is the center, the focal point of human history, and all of human history prior to the coming of Jesus Christ was a preparation for His coming:
After human beings rebelled against God and lost their original favor with Him, death and suffering entered into their world, God, not wanting His people to perish forever, was merciful and immediately made a promise that he would eventually redeem them through the woman's seed (Gen 3:15). God initiated and fulfilled his redemptive promise through the establishment of covenants with humanity:
1) His covenant promise to Abraham, the chosen line through which the Redeemer would come, introduced His merciful, sovereign and infallible determination to rescue a multitude of fallen sinners, by grace alone through faith alone (Gal 3:8).
2) In His covenant promise to Moses, God established His unchangeable Law (or eternal moral principles) that humanity must meet in order for that redemption to actually be completed. But no man having the moral capacity to do so...
3) God made provision for sinful humanity by fulfilling the righteous requirements of the Law in Jesus Christ. As a man, Jesus' full obedience to all the prescriptions of the divine law made available a perfect righteousness before the law that is imputed to those who, by grace, put their trust in him. Likewise his willing obedience in fully absorbing all the sanctions imposed by that law against his people due to their transgression is the ground of God’s justification of sinners (Rom. 5:9) and by which they are fully pardoned. In doing so He also fulfilled God's original promise to Abraham that "all nations on earth will be blessed through him." (Gen 12:3; 18:18; 22:18)
God rescues His People by His Holy Spirit bringing them into union with Christ. For if we belong to Jesus Christ we are indeed Abraham's offspring, heirs according to promise (Gal 3:29). "For no matter how many promises God has made, they are "Yes" in Christ. And so through him the "Amen" is spoken by us to the glory of God." (2 Cor 1:20)
Being adopted in Christ as God's children we are given new hearts (Ezek 36:26) and as new creatures live under grace in the New Covenant in Christ's blood through which we know God and have fellowship with Him. God's law is now written on our hearts, a law of love which works through us by the power of the Spirit who now dwells in us - the life of Christ Himself.