Every man or woman born into this world is born with what the scriptures call the Light of Christ or the Spirit of Jesus Christ (D&C 84:46; Moroni 7:16; John 1:9). The Light of Christ is the means by which the cosmos is ordered, the power and force by which the laws of nature exist and hold sway in the universe (see D&C 88:6-13). This same light is planted in the spirit of man by a benevolent God and serves as the source of reason and conscience and discernment.
It is a moral monitoring device, a directing and guiding influence which will strive with men and women and lead them to do good and choose righteousness if they will but acknowledge and respond to the soft inner impressions of this light … . if men and women in the world will respond to the quiet promptings and subtle whisperings of the Spirit of Jesus Christ within them, they will be led, either in this life or the next, to that higher light of the Holy Ghost found only in the covenant gospel through membership in the Lord’s Church. (Joseph Fielding McConkie and Robert L. Millet, The Holy Ghost, p. 6.)