As a pastor, "Why am I here?" is a common question that I get all of the time. It is a question about personal purpose. The question of "Why are we supposed to make disciples?" clues us in on the fact that we already know one of the great purposes of the church. It is simply a matter of understanding the reason behind it and following through. So why should we do it?
It is a matter of our nature. We make disciples because it is at the heart of who we are as the people of God. The theme of sending can be seen throughout the Bible and especially in the New Testament. After Jesus was risen, in John 20:21, He said, "As the Father has sent me, even so I am sending you." The sending nature of God and the sent nature of the church to the whole world are so that more and more people can be invited into the kingdom of God. Jesus wants everyone to know Him personally.
It is to be obedient to Jesus. We are to make disciples because Jesus told us to do it. The central idea of The Great Commission to the church in Matthew 28:18-20 is to "make disciples of all nations." In the other commissions by Jesus, we are given similar guidance from Christ. Acts 1:7-8 tells us that we will be His Spirit-empowered witnesses of Jesus. Luke 24:46-47 says that the gospel of His resurrection should be proclaimed to everyone.
It is so we can imitate Jesus. He did it. The early church did it. And we're supposed to do it. We want to be like our Savior who was constantly showing people how to follow Him. He did in all sorts of ways. He directly taught people to follow. He invited Himself over to a few of their houses to discuss it. He even described Himself with terms like Shepherd, Door, Water of Life, and the Way in order for people to understand what it means to follow Him. If you want to be like Jesus, then help people know who He is.
It is to help people avoid darkness. The only true way to know the light of life is to personally know the Author of life. The Bible goes to great lengths to show us that those who do not know Christ are currently in darkness—morally, relationally, and spiritually. They don't have the light of His presence and guidance. Even more dire is the eternal darkness that awaits those who are not Christians. When we say "no" to disciple-making, we are saying that the eternal destiny of people is not important to us. It was supremely important to God... so He died for us so we could live in the light of His presence.
It is for the glory of God. The act of making a disciple is one of the great ways that we make Jesus famous. It is how we lift Him up as most important. G. Campbell Morgan was a great preacher of the early 20th century and once said, "The greatest passion of the heart of Christ was not the saving of men but the glory of God, and then the saving of men because it is for the glory of God." The act of telling someone how to follow Jesus is not just to get another member in your church. By doing so, you are glorifying God in the world today.