This statement by Jesus defines his life and purpose.
Jesus said this to his students after washing their feet and explaining how becoming one of God's humble loving servants is the key to pleasing God.
Jesus did not come to the planet to 'die for our sins' as many professional ecclesiastical sectarian teachers profess.
Jesus came - as sent by the Supreme Being - to introduce us to God. He came to teach us how to re-establish our loving relationship with the Supreme Being. He came to illustrate the methods by which one can come to know the Supreme Person.
This statement by Jesus illustrates this precisely. If Jesus came to 'die for our sins' then he would have said so. He would not have spent years walking through the countryside teaching people about God. He would not have taken on students and specifically taught them about how they could learn to love God and then told them to go out and teach the same things to others. He would not have instructed them to serve God:
"Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven." (Matt. 7:21)
Doing someone else's "will" means to please them.
Jesus wanted those he taught to become God's servants, and thus return to God within the spiritual realm.
Doing someone else's "will" also requires we know what pleases them. This was another purpose for Jesus' teachings. He taught his students what pleases the Supreme Being.
Doing someone else's "will" and abandoning our own will out of choice means that we care for that person. Jesus taught his students to care for God, and to love God with every part of their being:
"'Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment." (Matt. 23:37-38)And Jesus taught that loving God means to revere the Supreme Being, and praise Him and His Holy Name:
"Our Father in heaven, hallowed be Your Name" (Matt. 6:9)