We are your reason, you are ours. by David Harwood

Reasonable.
 
For we write nothing else to you than what you read and understand, and I hope you will understand until the end; just as you also partially did understand us, that we are your reason to be proud as you also are ours, in the day of our Lord Jesus. (2 Corinthians 1:13-14)

... to be proud - Greek - to boast

We have an opportunity to contribute towards others’ rewards.

These verses speak of our being proud of one another at the judgment. 

I can understand the apostolic position: "I will be rewarded for establishing these believers." However, here the mutual support means that the church also receives a reward for the success of the apostolic mission.

We’re very connected. 

We actually share in the eternal rewards one another receives.