Paul emphasizes generosity. Mormon makes a different point: that God receives a gift depending on the giver’s intent. Where Paul encourages giving, Mormon emphasizes that, without the right motivation, the gift has no value to God.
Mormon is setting a very high requirement for church members. Tithing paid with a grudging heart is counted as though we had never paid it at all. Attending church meetings without the right spirit is the same as staying away. Of course, there is value in practice, repetition, and working dutifully through low points in our lives. Certainly there is a point to praying even when our heart is not completely in the right place. Brigham Young said of such occasions: “If I do not feel like praying, and asking my Father in heaven to give me a morning blessing, and to preserve me and my family and the good upon the earth through the day, I should say, ‘Brigham, get down here, on your knees, bow your body down before the throne of Him who rules in the heavens, and stay there until you can feel to supplicate at that throne of grace erected for sinners.’”
But this is not the message Mormon is stressing. Rather, he emphasizes the need to achieve the state where we not only act the right way, but we are the right way. Mormon’s context is the Savior’s Sermon at the Temple, where the Messiah used several examples to show that one’s intent should be toward God and not for the accolades of men (3 Ne. 13:1–6, 16). Mormon’s sermon follows that theme. God does not receive prayer whose purpose is to communicate a message for other men. It might well achieve that purpose; but for the higher function of communicating with God, we need to have true intent.
Brigham Young’s instructions are not addressed to those who are praying to impress others, but rather to those who are neglecting prayers that they know they should offer. He is telling us that at times we must work to pray with full intent, even if it is not there when we begin our prayers.