3 Nephi 18:13 - What does God mean when He says that we should not do "more or less" than what He asks us to do?

How do we make sure that we are following God's commandments perfectly without doing "more or less"?

D&C 93:24 states: "And truth is knowledge of things as they are, and as they were, and as they are to come; And whatsoever is more or less than this is the spirit of that wicked one who was a liar from the beginning."

Elder Stephen E. Robinson stated: "In the context of the gospel, truth is what God has actually said, what he actually directs, what he actually requires—no more and no less. On a strait and narrow path (see D&C 132:22), it doesn’t matter whether we fall off to the right or to the left, we are in trouble either way. It doesn’t matter whether we are 'liberals' or 'conservatives,' whether we believe 'too little' or 'too much'—that is, if Satan can’t get us to abandon the principles of the gospel, he is content that we should live them obsessively or as fanatics. One is less than the will of the Lord; the other adds human requirements to his will. Either puts us in the territory of the wicked one. There are those today who are embarrassed that God and his servants have said so much on some things and who go about trying to discredit the Brethren and neutralize the revelations and commandments. We have others who are embarrassed that God and his servants have not said more on other things and who go about preaching principles and programs the Lord has not revealed. One takes words out of God’s mouth; the other puts them in. Each preaches a 'new, improved' gospel inspired by that wicked one who was a liar from the beginning, the very first alternate voice. It requires discipline to embrace as gospel and to teach as gospel exactly what the Lord has revealed, no more and no less, and to avoid revising the gospel to suit ourselves. But those who can do it will know things as they really are (see Jacob 4:13) and will avoid deception" (Ensign, "Enduring to the End," October 1993).

The gospel is simple. We can know exactly what the Lord wants us to do because of the commandments he has given us. Elder Henry B. Eyring said, "You will notice that the work is simple obedience. It is not complicated things; it is not fancy things or getting great spiritual manifestations" (Ensign, "A Life Founded in Life and Truth," July 2001).

The Spirit is what guides us to know what is right and wrong. President Joseph Fielding Smith said, "Every man has a conscience and knows more or less when he does wrong, and the Spirit guides him if he will hearken to its whisperings" (Doctrines of Salvation, comp. Bruce R. McConkie, 3 vols. [1954–56], 1:51.) We can all know the Lord's will by listening to the promptings of the Holy Spirit and obeying with exactness.