Verses 16-18 comprise a unit on fasting. This is another devotion directed to God, and becomes yet another case where the essential antithesis is the public versus private. In fact, verse 18 ends with the same phrasing that we have seen in 3 Nephi 13:4 and 6. The Lord sees in secret, and rewards openly. Once again the emphasis is on the internal reasons for the devotion rather than the external. As with the other examples, it is assumed that one will fast, and that the fasting will garner a reward. The difference continues to be that an act done for men receives a reward of men. The act done where only God can see will receive a reward of God.
Old World Context: The traditional context of fasting was one of emphasis on deprivation. It frequently accompanied mourning, and was therefore considered appropriate for festival occasions that recognized national calamities (Robert Guelich. A Foundation for Understanding the Sermon on the Mount. Word Publishing, Dallas. 1982, p. 298). It is the context of calamities or other afflictions that influenced the cultural attitudes towards fasting. Since it was typically found in contexts of mourning for something if not someone, then it was appropriate to appear as if in mourning. Hence the public attire reflecting an attitude of mourning.
When Jesus counsels on fasting, he is shifting the reasons for fasting from one of affliction to one of spiritual preparation. Thus for Jesus, fasting is not mourning, but spiritual purification. It is therefore appropriate for them to anoint themselves rather than take on the visual aspects of mourning. The combination of fasting and prayer was an understood intensifier of prayer in Judaism (Robert Guelich. A Foundation for Understanding the Sermon on the Mount. Word Publishing, Dallas. 1982, p. 299). This is the context in which it functions for Jesus. The difference was not in the function, but in the visual presentation. For Jesus, fasting could be integrated into one’s life as a regular part of one’s spiritual preparation.
The Pharisees fasted twice a week. (Robert Guelich. A Foundation for Understanding the Sermon on the Mount. Word Publishing, Dallas. 1982, p. 298). It is probable that Jesus performed some type of regular fasting. The best proof of this is the occasion of the healing of the young man after the failure of the disciples to accomplish the healing:
Matthew 17:19-21
19 Then came the disciples to Jesus apart, and said, Why could not we cast him out?
20 And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
21 Howbeit this kind goeth not out but by prayer and fasting.
On this occasion, the apostles certainly were faithful, but yet unable to perform the healing. When Jesus arrives, he is able to immediately perform the healing. He does not say, I must fast, and leaves to fast for a period of time. What he does is perform the healing as assure the twelve that this additional capability was due to fasting. That fasting had to have been performed prior to that event, and as part of a continuous process of spiritual preparation.
Book of Mormon Context: The Book of Mormon context of fasting includes both the aspects of mourning (Alma 28:6; Alma 30:2) and spiritual preparation in conjunction with prayer (Alma 6:6; Alma 17:3). What is not know for the Book of Mormon is whether or not there were visual manifestations of fasting or mourning. Because we do not know if there was a visual component of fasting in the New World, the applicability of this particular part of the Sermon to the New World context is unknown.
Textual: There are no changes from the Matthean text.