There are a few promises in the Book of Mormon that are repeated over and over again. This promise is a marvelous promise with grand and eternal implications too often taken for granted. When the Lord promises to give us whatever we want, which is good, as long as we ask in faith believing in his name, he means what he says. We have no reason to doubt, no reason to waver—else we become like a wave of the sea driven with the wind and tossed (James 1:6). See also commentary for 3 Nephi 18:20.
Neal A. Maxwell
"By praying, we begin to experience what it is like when we see the interplay of man‘s moral agency and God’s directing hand. These are things to be learned only by experience. We learn how important our intentions are, since we are instructed to pray for that ‘which is right’ (3 Nephi 18:20). Our prayers will be better if they are in fact inspired prayers.
“Thus worshipping, serving, studying, praying, each in its own way squeezes selfishness out of us; it pushes aside our preoccupations with the things of the world.” (Men and Women of Christ, p. 98)