What is the significance of 21 days of fasting?
Four of us are fasting and praying for the anointing of the Holy Spirit, our families' salvation and for our friends nearby. I saw on your web site about the importance of 40 days and thought of asking you.
Under the Old Testament, God commanded fasting for certain days, but they were only one day in length. When Esther was concerned about approaching the king about the order for killing the Jews, she asked that her friends pray and fast for three days (Esther 4:16). Jesus fasted for forty days in the wilderness prior to his temptation, but that is unusually long (Matthew 4:2). There is no mention of a twenty-one day fast in the Scriptures.
There is no requirement in the New Testament for fasting, though there is no restriction on fasting if a Christian desires to do so. Many people don't understand the purpose of fasting. You can read more about it in "Should Christians fast?"