Faith does not add to salvation but through faith we trust Christ who is our Salvation. We see the grace wherein we stand. Thusly, the law is not made void but in every way established.
Faith establishes the law as the embodiment of Gods character. A believer knows what the law of God requires thus seeing God as holy, holy, holy. What righteousness!
Faith establishes the law in that the law finds natural man totally unrighteous, unfit, incapable of approaching God. for by the law is the knowledge of sin. (Rom 3:20) Saving faith compares my deeds to what the law demands, showing me my need of a substitute.
Holy law is a magnificent steed
Too many hands high
For me to mount and ride to glory
No matter how I try
Faith establishes the law as the witness to Christs perfect obedience. Made of a woman, made under the law, Christ fulfilled the law in every respect. The sinner saved by grace delights to hear the law declare Christ righteous for He is our Righteousness.
Faith establishes the law as a witness that God is both just and justifier. The law reveals sin in us and the wages of sin are death. God can in no wise clear the guilty. But by the wisdom of God, Christ is the spotless Lamb, set forth to be the propitiation through faith in His blood.
Faith establishes the law because the believers sincere desire is to obey the law for the sake of Christ who loved us and gave himself for us. Not that we might obtain a righteousness; our righteousness has been obtained. Not that we might become holy; in Christ we are holy. But rather, the true desire toward obedience to God in every believer is the fruit of the Spirit with which we have been sealed. Because of all that Christ has accomplished, God by the work of the Holy Spirit, writes his law upon the heart of every believer. There is no longer a spirit of bondage but a spirit of adoption, whereby we desire to be like Christ. And thanks to the faithful Abba, Father in which we worship, one day we will.