Think about it like this....Jesus could have taught every sermon and parable in his ministry without the 12 disciples being around. In fact, Jesus could have healed, spoke truth to the Pharisees, died for our sins, and rose form the dead...all by himself. Jesus could have had a dynamic ministry without ever discipling anyone.
So why invite 12 guys to follow you around and give them access to your life? The answer is this: Jesus wanted to build more than a dynamic ministry, he wanted to build a movement. In order to build a movement that outlives the founder, you have to make disciples. Ministry is not enough. Some churches have dynamic ministry going on, which is great! God will move in and among his people when we obediently serve people. But without disciple making, it will never be become a movement, and you will likely be limited in the amount of ministry you will be able to do as well. After all, who is going to lead those ministries? Who will lead new ministries? Who is going to minister to the people you reach through those ministries? Without making disciples, you will not be able to develop leaders, and without leaders, ministry can only go so far.
However, if you make disciples, then you will get more ministry, and the people who come into the orbit of that ministry will come into contact with people who can make disciples, and this will eventually lead to more ministry and missional ventures in the long run. Sounds simple, sounds cute and trite, but don't be fooled. This is really how it works.