Reason Paul may seem strained, because he was on the receiving end and had nothing to give in return. But he doesn't need it anyway. This is the strongest glue any friendship can have. Their gifts were a symbol of the reality of feeling. C. Mutuality also works on higher level - our relationship with God.
Christian sharing is never one way.
When we give, we can expect something in return. Now, you have to be careful with this or it can get a little crass. But the general principle is very Biblical - sharers get back more than they give. Picture is of a grain marketplace, with grain heaped in your lap. When God is in charge, there is no settling of contents due to handling.