2 Nephi 32: 4-5

“Wherefore, now after I have spoken these words, if ye cannot understand them it will be because ye ask not, neither do ye knock; wherefore, ye are not brought into the light, but must perish in the dark.  For behold, again I say unto you that if ye will enter in by the way, and receive the Holy Ghost, it will show unto you all things what ye should do.”
 
Comprehension of the “doctrine of Christ” is not based on command of a vocabulary or mastery of an argument. It is based on gathering light. Light is gathered by heed (obedience) and diligence alone. (D&C 130: 19.) By following the light you have received already, you grow in light. (D&C 50: 24.) This process leads to the “perfect day” where the light has chased away all darkness. This is how we, like Christ, can grow from grace to grace until we also receive a fullness. (D&C 93: 20.)
 
If you do not do this, then you may acquire a vocabulary with which to discuss the subject, but you will not have the light to comprehend it. Light can be shining all around you, but if you do not acquire light within yourself by your actions, you cannot comprehend the light.  (See, e.g., D&C 6: 21; D&C 10: 58; D&C 34: 2; D&C 39: 2; D&C 45: 7; and D&C 88: 49.)
 
If it perplexes you, then ask God for understanding. He will tell you what to do.  Follow His instruction. In this way you qualify to receive further light and knowledge by conversing with the Lord. He knows perfectly what you lack, and by the Holy Ghost within you will tell you what you must do.

If you will not humble yourself and ask for this to be made known to you, then you cannot be brought into the light. Then the only result will be to perish in the dark.

If you will follow the steps with the required real intent, acting no deception before God as you do, then you will receive the Holy Ghost.  It will be unlocked to tell you what you lack and what you need to do. This inner light is a powerful source which can literally tell “you all things what ye should do.”

 
It is in the doing that you find the learning.  It is in the act of following Him that you learn to be like Him. Obedience is the means by which you gather light. The commandments are revelations of the inner person you ought to become. They are how you grow in the flesh to comprehend God in the Spirit. Your body is a veil that keeps you from Him. By subordinating the will of the flesh to the will of the Spirit, you gain light and truth.
 
Do it to understand it.
 
Once you understand you will be able to tell when someone speaks with the power of the Spirit words of eternal life, or if they are, as Nephi puts it: “perishing in the dark.”  There are many who claim to speak on the Lord’s behalf who declare false, vain and foolish things. While they will be held to account for that, the point is not to condemn them. They may yet see the light, and repent and return.  The point is that you must avoid being misled by those who would lead you astray. The few humble followers of Christ are warned that they will be taught the precepts of men and must use caution to avoid being misled. (2 Nephi 28: 14.) We’ve discussed that already.
 
The proportions and the balances required to see things aright are too fine, too subtle and too difficult to put into words. They are harmony. Nephi’s teachings are woven into one great whole. There are not isolated strains to be taken from the great whole and then given undeserved importance. They must fit together. You can only accomplish that when you see the whole by the light of the Holy Ghost within you.
Nephi is both pleading and warning in these two verses. He wants you to go to the source and be directed from there. To have the words of Christ available to you. To hear the words of angels as you draw near to the light. If you do not, then it is because you refuse to follow the steps he has described.
 
You must act to know. Without following through in your heart (which you cannot ever deceive) you can’t draw near to the light. The discussion in The Second Comforter walks through line upon line that walk back into the light, and ultimately into Christ’s presence.  It is a modern manual to find Him.