This is Mormon’s extrapolation from the lesson of the scriptures. The reference to the evil man who gives a gift is part of the Lord’s sermon in Bountiful, but the grudging giving is not. There is a similar teaching in the New Testament, but it is not in exactly the same terms or context:
2 Corinthians 9:6-7
6 But this I say, He which soweth sparingly shall reap also sparingly; and he which soweth bountifully shall reap also bountifully.
7 Every man according as he purposeth in his heart, so let him give; not grudgingly, or of necessity: for God loveth a cheerful giver.
The intent of the 2 Corinthians passage is to emphasize the generosity. In Mormon, the text is given to indicate that the reception of a gift to God depends upon the intent. Where one encourages giving, the other (Mormon) emphasizes that giving must be done with a certain intent, or it is of no value to God.
Mormon is setting a very high requirement for the saints of the church. He is telling us that when we pay our tithing with a grudging heart, it is counted to us as though we had never paid it all. When we attend our church meetings, it is as if we had not at all if we do not bring the right spirit with us. Of course there is value in practice, repetition, and in working through low points in our lives, but that is not his particular message. Mormon is emphasizing the need to achieve the state were we not only act the right way, but we are the right way.