Talk about "working together." Note the complimentary way Paul and the Corinthians shared in ministry. They prayed for him and he really felt the effectiveness of their prayers. Meanwhile, he and his companions, had a big part in working to see the believers in Corinth truly have joy in their lives. And they likely reversed roles as well for certainly Paul prayed much for them and they brought Paul to great joy as he saw their spiritual growth and involvement in Christian work.
This is an ideal relationship between believers whether it be the pastor and congregation or fellow Christian workers with others in ministry. The two questions that arise out of this are: one, do we really pray for one another to be effective in ministry?; And, two, do we really help others be filled with joy by our ministry to them?