And Christ gave his authority to the apostles, the first Bishops.
Where in the Scripture you posted, does Christ give His authority to anyone? He gave them a charge and promised to be with them to the end of the age.
Also, you add bishops to the Disciples in your understanding. Really Christ is speaking to them of the whole Church which was to come, which they represented.
Even right now you are trying to teach. Are you a Bishop? Is Christ with all Christians always or only the Bishops of the CC?
Mat 28:18 And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth.
Mat 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Mat 28:20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.