What is the focus of our religious acts? Jesus, in Matt 6:1-18, is teaching His disciples about the nature of His kingdom, the kingdom of heaven. Jesus has been describing for them the kingdom in terms that declare it to be the opposite of what they expect it to be.
If they expect the kingdom to be by human force or effort, and they did (Luke 9:46–48; 22:24–30; John 6:15), then they misunderstand the nature of the kingdom of heaven. The kingdom of heaven belongs to those who are poor in spirit et al. (Matt 6:3–10). The kingdom would surpass their expectations in that it fulfills the law (5:17) and goes beyond the requirements of justice in the law, eye for an eye (5:38). The kingdom of heaven seeks not to establish justice, as the law had done, but to express the victory found only in sacrifice. The kingdom confers the sacrifice of going the extra mile (5:41).
The extra mile in regard to giving (Matt 6:1–4) is for it to be done in secret, without the attention of men. The extra mile in regard to prayer is for it to be done before God, in secret, not to be seen by men (6:5–13). The extra mile in regard to fasting (denying self) is for it to be done so that it is only obvious to God (6:16–18).
“When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show men they are fasting. I tell you the truth, they have received their reward in full. 17 But when you fast, put oil on your head and wash your face, 18 so that it will not be obvious to men that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you (Matt 6:16–18 NIV).
The outward disciplines of giving, prayer, and fasting that the Jews expected of any faithful Jew were to find their fulfillment in the kingdom in ways that did not look to men for reward but to the Father in heaven. These disciplines were to be practiced in the kingdom in ways that brought glory to God by placing God above all else in the mind of the disciple! The objective of these disciplines was to focus the thoughts of the disciples on their reward from their Father in heaven (6:4,6,18).
The desire of God is for all men to be saved (1 Tim 2:4) and for those who are saved to be created/conformed into the likeness of His Son (Rom 8:29; Eph 4:24). Therefore, the commandments He gives us should bring us to know Him (John 17:3) and escape the corruption of the world caused by evil desires (2 Pet 1:3–4). Fasting (denying self), praying, and giving should discipline us to look beyond this life for our reward!