You are called, you are commissioned ,by Jesus, to bear witness to Him. What bothers me, is that in Christian circles, those two words have become synonymous. That's not the same thing as saying that all Americans are Floridians. There are 49 other states you could be from. All evangelism IS witnessing, but not all witnessing is evangelism.
Evangelism is a species of witnessing.
We are all called to witness, and we are all called to make sure we support all the other tasks and ministries so that they too are accomplished. But, Paul is clear to say that we should not think more highly of our own gift than we should. The spirit of love and charity which should be in our heart means that rather than exalting our own situation, our own life, or our own gift, we should honor the gifts and talents of our brothers and sisters. Paul moves on to talk about the harmony that should exist between the different gifts. If a man's gift is prophesying, let him use it in proportion to his faith.