The law of God is the embodiment of the knowledge and truth which defines how to love both God and our fellow man, but that definition of love is incomplete when grace is excluded from it, because grace informs us that God still loves us perfectly, even when we fall short of the standards set by the law. Conversely, however, grace becomes superfluous apart from the law, since no pardon is required where no transgression exists.
The law is exemplified in the Old Testament; grace is revealed in the New. Both are essential and requisite in order to understand the mind of God accurately. Jesus, the Christ, embodied the law and fulfilled its requirements in his life; then gave the fullest expression to grace through his death, by paying the penalty the law demands, on our behalf. Having paid that penalty, once, for all, death itself ultimately died along with him — but the law itself did not pass away.