At some point in the past, humanity chose to depart from God's will and began to sin.
Because no one is free from sin, people cannot deal with God directly, so God revealed Himself in ways people could understand.
God called Abraham and his progeny to be the means for saving all of humanity.
To this end, He gave the Law to Moses.
The resulting nation of Israel went through cycles of sin and repentance, yet the prophets show an increasing understanding of the Law as a moral, not just a ceremonial, force.
Jesus brought a perfect understanding of the Mosaic Law, that of love and salvation.
By His death and resurrection, all who believe are saved and reconciled to God.