2007 was my first year in Bible education in the United States. I heard a professor say that the “doing the will of my Father” in Matthew 7:21 is to be baptized in the mode of immersion, absolutely in the name of Jesus. It was kind of eye-opening teaching for me. I was so impressed by the simplicity of the ‘truth’ and became a zealous ‘evangelist’ of that ‘truth’. My energetic evangelism in it led several people to the baptism in the year. I was a John the Baptist, who preached the ‘truth’. Do I believe it now? Sort of not; very soon I became not to think of the passage that simple. Then, what is “the will of the Father” that Jesus teaches?
To answer the question, we have to look at the context around the passage, which is the Sermon on the Mount and also that of the New Testament. The main message of the Sermon is love, not immersion in water. For instance, “good works” in 5:16, which disciples have to do to be salt and light to the world, should be (out of) love obviously; we should have love to our brothers, even to our enemies, instead of anger or enmity (5:21-48); we have to forgive others out of mercy (6:16-18); we should love God instead of worldly things (6:24); and we have to do for others what we would want others to do to us in the situation, which is the definition of love and is the fulfillment of the Law and the Prophets (7:12). After all the teachings like these, Jesus teaches to do the will of the Father in heaven in 7:21-23. So, according to the context of the Sermon, it is obvious that doing the will of the Father means to love, not immersion in water. Actually this also coincides with Jesus’ only “new commandment”: “Just as I have loved you, love one another” (John 13:34). Paul also teaches that love is the fulfillment of the law (Rom. 13:10; Gal. 5:14; cf. 1 Cor. 13:1-3). Hebrews writer (13:1f), Peter (2 Pet. 4:8), and John (1 John 3:11f) do the same.
On this interpretation, I believe, doing the will of the Father in Matthew 7:21 is more to love than to be baptized. Whatever we may do have to be out of our genuine love of God and brothers. Even water baptism without love in heart is nothing (1 Cor. 13:1-3). This is significant for our evangelism also. It tells us what to preach and what to convert people into. We have to teach people what Jesus taught us to do (Matt. 28:20) to be salt and light, that is love. We have to convert first ourselves and others into the love that the Father in heaven commanded us to have/do—and nothing else. Water baptism should be the expression of rebirth for the love in heart (1 Pet. 1:22). This is the truth of God, because God is love (1 John 4:8) and what Jesus manifested of God by His life unto death is the love (Rom. 5:8; 1 John 3:16). As only Jesus’ love saves, we are to be evangelists of the love—having born of and living by it.