Have We Not Reason To Rejoice

D&C 59 13-14 :

13 And on this day thou shalt do none other thing, only let thy food be prepared with singleness of heart that thy fasting may be perfect, or, in other words, that thy joy may be full.

14 Verily, this is fasting and prayer, or in other words, rejoicing and prayer.

Deut. 12:7:


7 And there ye shall eat before the LORD your God, and ye shall rejoice in all that ye put your hand unto, ye and your households, wherein the LORD thy God hath blessed thee.