Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life. (John 8:12)Jesus gave this same declaration before Jesus appeared to the Nephites they heard his voice declaring this (3 Nephi 9:18) as well as when he appeared to the Nephites (3 Nephi 11:11).
The Metaphor of Light
I have always love the metaphor of light and have thought about it's meaning a lot. Light refers to truth and intelligence (see D&C 93:36). There are a lot of references to light being truth:
4 In him was life; and the life was the light of men.5 And the light shineth in darkness; and the darkness comprehended it not.Doctrine and Covenants 93:28
28 He that keepeth his commandments receiveth truth and light, until he is glorified in truth and knoweth all things.Light not only refers to truth, but also represents works or deeds. In the Sermon on the Mount, Jesus, in speaking to his disciples, stated the following:
14 Ye are the light of the world. A city that is set on an hill cannot be hid. 15 Neither do men light a candle, and put it under a bushel, but on a candlestick; and it giveth light unto all that are in the house.16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven. (Matthew 5:14-16)Here Jesus is using the word light to refer to works. The purpose of these works are to help others focus on Christ and glorify the Father.
Therefore, hold up your light that it may shine unto the world. Behold I am the light which ye shall hold up—that which ye have seen me do. Behold ye see that I have prayed unto the Father, and ye all have witnessed. (3 Nephi 18:24)These two metaphors are inherently connected though since works need to be based on truth. Our works should be truth in action.
Christ is the Light
So, if light refers to truth and works, how is Christ the light?
6 He that ascended up on high, as also he descended below all things, in that he comprehended all things, that he might be in all and through all things, the light of truth; (Doctrine and Covenants 88:6)Christ descended below what anyone else has descended, which enabled him to ascend beyond anyone else. Each time we ascend, we comprehend more truth. Because he has ascended higher than anyone else, he comprehends more truth than anyone else. This is why he can be called the light of truth.
7 Which truth shineth. This is the light of Christ. As also he is in the sun, and the light of the sun, and the power thereof by which it was made. 8 As also he is in the moon, and is the light of the moon, and the power thereof by which it was made; 9 As also the light of the stars, and the power thereof by which they were made; 10 And the earth also, and the power thereof, even the earth upon which you stand. 11 And the light which shineth, which giveth you light, is through him who enlighteneth your eyes, which is the same light that quickeneth your understandings; 12 Which light proceedeth forth from the presence of God to fill the immensity of space—13 The light which is in all things, which giveth life to all things, which is the law by which all things are governed, even the power of God who sitteth upon his throne, who is in the bosom of eternity, who is in the midst of all things. (Doctrine and Covenants 88:7-13)If faith is belief combined with revelation (i.e. truth), then as one acts on this truth (i.e. performs works), power is given. (This is from Joseph Smith's lectures on faith. See this post for an explanation.)
As Christ comprehends all truth (in his sphere), he possesses all power. So, as he speaks, things are able to be organized and governed, such as the earth and sun. So, another dimension to this light is power, as verse 13 states. If you want to understand this more, study Doctrine and Covenants 93.
As we understand more truth and perform the works the Lord wants us to do, we obtain more light.
24 That which is of God is light; and he that receiveth light, and continueth in God, receiveth more light; and that light groweth brighter and brighter until the perfect day.25 And again, verily I say unto you, and I say it that you may know the truth, that you may chase darkness from among you; (Doctrine and Covenants 50:24-25)The perfect day is when we are able to stand in the presence of the Lord and obtain knowledge. The way to get there is to obtain truth and to perform works based on that truth (which usually involves lots of repentance).
28 He that keepeth his commandments receiveth truth and light, until he is glorified in truth and knoweth all things. (Doctrine and Covenants 93:28)Using the light to point to Christ
When we obtain light, we can use it to point to ourselves and how wonderful we are, or we can reflect this light onto Christ, giving him the glory, thus pointing others to him.
True messengers and true messages conform to a pattern mentioned in 3 Nephi 18:24 which we read earlier, which stated “I am the light which ye shall hold up.” They help the people focus on Christ rather than on themselves or another man:
Every thing which inviteth to do good, and to persuade to believe in Christ, is sent forth by the power and gift of Christ; wherefore ye may know with a perfect knowledge it is of God. But whatsoever thing persuadeth man to do evil, and believe not in Christ, and deny him, and serve not God, then ye may know with a perfect knowledge it is of the devil. (Moroni 7:16)The opposite of this is priestcraft.
He commandeth that there shall be no priestcrafts; for, behold, priestcrafts are that men preach and set themselves up for a light unto the world, that they may get gain and praise of the world; but they seek not the welfare of Zion. (2 Nephi 26: 29)Priestcraft is where someone wants to be in charge and have control over other people, setting themselves up as that person at the head, saying, “Follow me” instead of pointing to Christ. Someone who is engaging in priestcraft doesn't have to explicitly say "Don't follow Christ; Follow me!" But, anytime someone points to another man or woman to follow, instead of Christ, they are are taking the attention (or the light) off Christ. This really is the essence of idolatry, because this an indirect invitation that says: Don't look at Christ; look at me!
What works should be performed?
Further on in the Sermon on the Mount, Jesus talks more about these works that his disciples needed to display in order to bring people to Christ. Read Matthew 7:15-23 where fruit is used as a metaphor for these works.
15 Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves.16 Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles?17 Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.18 A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.19 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.20 Wherefore by their fruits ye shall know them.21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.Jesus says to beware of false prophets. What would a prophet's fruit be? Think in terms of light being truth and works (bring forth new revelation/scripture/visions/prophecy – truth; perform mighty miracles in public, such as heal the sick, raise the dead – works; etc)
Here we have a group of men called to be Christ's first apostles. Jesus was teaching them about the necessary fruit or works they needed to produce if they were to be considered prophets. He was teaching them not to be false prophets. Throughout the Old Testament we learn of prophets who didn't prophesy. There were no works. This led the people to err or go astray (see Isaiah 9:15-16). Jesus wanted them to make sure they obtained these gifts and led others to Him through their truth and works.
Those who try to lead without truth and works are essentially blind guides (see Helaman 5:29). And those who follow them have set those leaders up as a light, instead of Christ. We need to examine anyone carefully who desires to lead us and determine is they are setting themselves up as a light or have not truth and works. The point is to always focus on Christ, who is the true Light. Then, as we obtain truth and perform the associated works, we obtain light, but we then use this light to point others to Christ.