He understood we are all members of Christ.

Acts 15:36-39
After some time Paul said to Barnabas, “Let’s go back and visit each city where we previously preached the word of the Lord, to see how the new believers are doing.” Barnabas agreed and wanted to take along John Mark. But Paul disagreed strongly, since John Mark had deserted them in Pamphylia and had not continued with them in their work. Their disagreement was so sharp that they separated. Barnabas took John Mark with him and sailed for Cyprus.

Here we have a disagreement between the apostles,where Paul speaks ill of Mark. Apostle paul rejected servitude with Mark because Mark had left them(Acts 13:13) in their voyage.
Later,
2 Timothy 4:11 NLT
...Bring Mark with you when you come, for he will be helpful to me in my ministry.

Here Apostle speaks respectfully of Mark and even admits his need of Mark.
By this it appears that Paul was now reconciled to Mark, and had a better opinion of him than he had had formerly. This teaches us to be of a forgiving spirit; we must not therefore disclaim for ever making use of those that are profitable and useful, though they may have done amiss.
No matter who a brethren is or what he/she might have previously done that brought contention, that Saint is still in every way a part of you dear Christian brother and sister.