The Book of Mormon offers so much that broadens our understandings of the doctrines of salvation. Without it, much of what is taught in other scriptures would not be nearly so plain and precious.
That is, the only reason salvation is necessary is to get us back to the garden. The Pentateuch not only presents where we began but also why we are not there any more, and why and how we need to get back.
These are fountains of salvation that they who thirst may be satisfied with the living words they contain. In these alone is proclaimed the doctrine of godliness. Let no man add to these, neither let him take out from these.
Salvation is from our side a choice, from the divine side it is a seizing upon, an apprehending, a conquest by the Most High God. Our 'accepting' and 'willing' are reactions rather than actions. The right of determination must always remain with God.