Light of Christ

Mosiah 18:8-10
 8 And it came to pass that he said unto them: Behold, here are the waters of Mormon (for thus were they called) and now, as ye are desirous to come into the fold of God, and to be called his people, and are willing to bear one another’s burdens, that they may be light;
 9 Yea, and are willing to mourn with those that mourn; yea, and comfort those that stand in need of comfort, and to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death, that ye may be redeemed of God, and be numbered with those of the first resurrection, that ye may have eternal life—
 10 Now I say unto you, if this be the desire of your hearts, what have you against being baptized in the name of the Lord, as a witness before him that ye have entered into a covenant with him, that ye will serve him and keep his commandments, that he may pour out his Spirit more abundantly upon you?

Before we are baptized all people have the light of Christ to guide them in a basic way, much like what some call our conscience.  The feeling that tells us what is right and what is wrong.  After we are baptized we receive the gift of the Holy Ghost, which allows us to have a greater portion of those impressions from the Spirit if we are obedient to Heavenly Father.  These impressions guide us more deeply and more specifically as we make decisions in our life.