[Jesus said,] "Beware of practicing your righteousness before other people in order to be seen by them, for then you will have no reward from your Father who is in heaven.
"Thus, when you give to the needy, sound no trumpet before you, as the hypocrites do in the synagogues and in the streets, that they may be praised by others. Truly, I say to you, they have received their reward. But when you give to the needy, do not let your left hand know what your right hand is doing, so that your giving may be in secret. And your Father who sees in secret will reward you" (Matthew 6:1-4 ESV).
Jesus introduced a new concept to his followers when He instructed them to do their good deeds and kind acts in secret instead of making a who of it. He followed up this discussion with similar discussions on prayer and fasting (Matthew 6:5-18).. His message is simple: when you do these things, do them quietly and without drawing attention to yourself. Your Father sees. Your Father knows. Your Father will reward. But, all that is forfeited if we try to get our reward, our accolades, our praise, our reputation, on earth (Matthew 6:19-21).
Apparently, quiet goodness and anonymous good deeds were a problem for religious people in Jesus' day. Jesus criticized them for the way they loved to show off with their acts of worship. When they gave, they enjoyed people around knowing how generous they were. When the prayed, they loved to perform as if on stage using flowery and pious language, being long and repetitious, and making sure they were recognized for their godliness. When they fasted, they made sure everyone knew the sacrificial act of worship they were engaged in. Long faces. There was possibly moaning and groaning about the lack of food.
Jesus is basically saying to His disciples, "This is not the way we do things." The same wisdom should still apply.
As disciples of Jesus, when we do good things, we should just do them. It is not necessary to call attention to our good deeds. It is not necessary to get credit. It is not necessary to hear a "Thank you." It is not necessary to be repaid. If you intended to do a good thing, do not ruin it by letting everyone around you know what you did. It is enough for the Lord to be praised for the good you do (Matthew 5:16).
And when you fast, do not tell anyone. Do not announce it in your Sunday School class or small group. Do not ask them to pray for you because you are fasting. Wash your face. Take a shower. Keep a pleasant look on your face. If someone notices you not eating and asks you about it, just give them a polite, "I'm just not eating today" and be done with it.
For Jesus, and for Jesus' people, service, kindness, piety, and generosity are not about the show. It is going about one's life quietly, simply, and without drawing attention to what you do. It is not necessary to announce, "Hey everyone, I'm about to do something that looks like Jesus. Watch me!" Just be like Jesus. Let the show end.