Go and Make Disciples, in these three sections, looks at three additional reasons to evangelize. That’s other that because Jesus told us to.
Affirming the human person involves our heritage as people of God:
Unless people know the grandeur for which they are made, they cannot reach fulfillment and their lives will be incomplete. Nor will they know that they are called into interpersonal union with God and with each other. (GMD 31)
Christians still preach Jesus Christ:
The unique claim of our message does not negate the sincerity and faith of others; likewise, the sincerity and faith of others do not take away from the clarity and truth of our message. (GMD 32)
This is also a command of the Lord: love one another. Faith inspires love, and so the things we do in faith and for others reflect that love shown to us by God. If we experience it, do we pass it on? And if we don’t pass it on, have we truly experienced it?
Catholic Sensibility 