Col 3:12-17 / Luke 6:27-38
To act on behalf of someone would mean that the person have given you full authority to do whatever on that person's behalf.
This is often ratified by a legal document or some kind of recognized written permission by that person concerned.
This authority will stand as long as it is not revoked or legally revoked by the person.
In the 1st reading, St. Paul tells us that we are God's chosen race, His saints, and He loves us.
St. Paul also added that we should never say or do anything except in the name of the Lord Jesus.
So we have been given the authority and the power to accomplish what God has commissioned us to do.
When Jesus says in the gospel - Love your enemies, do good to those who hate you, bless those who curse you, pray for those who treat you badly - that would sound like humanly unachievable or even impossible.
But this is what Jesus entrusted us to do and to those whom He has entrusted, He has also empowered.
Whatever we do or say in the name of the Lord Jesus, God will also bring it to fulfillment and completion.
We need to ask Jesus to clothe us with sincere compassion, kindness and humility, gentleness and patience, and then we will have that power and authority to act on behalf of Jesus.