In Verse 12, Paul was referring to Ephraphas who was the minister in Colosse who had gone to Paul for wisdom and advice about the church. He tells us that Ephraphas agonizes deeply for the church always praying for them to grow.
It is very key for a leader/minister to have strong zeal for the work to which they have commited.
Luke, here mentioned, is the author of the book of Luke and the Acts of the Apostle. He was a doctor and a travelling companion of Paul.