Law of Moses brought believers to Christ

Alma 25 (http://scriptures.lds.org/en/alma/25) describes how after the
Lamanites converted to the gospel of Jesus Christ, they buried their
weapons of war and became a righteous people. They followed the law
of Moses. Although it did not provide them salavation, it did prepare
them and give them the hope for the coming of Jesus Christ.

14 And they did also bury their weapons of war, according as their
brethren had, and they began to be a righteous people; and they did
walk in the ways of the Lord, and did observe to keep his commandments
and his statutes.
15 Yea, and they did keep the law of Moses; for it was expedient
that they should keep the law of Moses as yet, for it was not all
fulfilled. But notwithstanding the law of Moses, they did look forward
to the coming of Christ, considering that the law of Moses was a type
of his coming, and believing that they must keep those outward
performances until the time that he should be revealed unto them.
16 Now they did not suppose that salvation came by the law of Moses;
but the law of Moses did serve to strengthen their faith in Christ;
and thus they did retain a hope through faith, unto eternal salvation,
relying upon the spirit of prophecy, which spake of those things to
come.