We keep the law of God strictly and perfectly through faith in the Lord Jesus Christ (Rom. 3:31). The law requires perfect obedience and perfect satisfaction. And all who trust the Lord Jesus Christ give the law what it requires. Christ, as our Substitute, magnified the law and made it honorable. He perfectly obeyed the very letter and spirit of God's holy law for us. Then he poured out his life's blood as our Substitute at Calvary, rendering perfect satisfaction to the law's justice. By his obedience being imputed to us, all who believe are made righteous before the law. As we read the law, we look to Christ by faith and keep the law.
We also keep the commandments of God personally. God's saints are not legalists. We do not live by the rule of the law. But we are not lawless. We delight in the law of God after the inner man (Rom. 7:22), keeping it in our hearts with joy. And our lives are governed by the Word of God, his revealed will, in its entirety. That which God teaches and commands, it is our delight to believe and do, because we love him (I John 5:1-3). The source and essence of the believer's obedience to God is faith in and love for Christ.