Works are the roots of faith. A system of beliefs that is not rooted in works of righteousness, like a tree whose branches have outgrown its roots, is vulnerable to uprooting by every wind of doctrine or ideological storm that comes its way. This is why the scriptures teach us that we can know the gospel only to the extent that we live it.
Joseph Fielding McConkie, “Seeking the Spirit”
To say that we believe in God is only half of the formula. If we say we believe in God, then He is also waiting to see if we'll act like we believe in God. Again, He knows our heart and if we are trying to be like Him.