A.T. Robertson Commentary 2 Corinthians 8:5

"and [this], not as we had hoped, but first they gave their own selves to the Lord, and to us through the will of God." — 2 Corinthians 8:5 (ASV)

We had hoped (ηλπισαμεν). First aorist active indicative of ελπιζω. "Expected," he means. They went beyond his hopes about them.

First they gave their own selves (εαυτους εδωκαν πρωτον). First aorist active indicative of διδωμ (k aorist). "Themselves they gave first." That is the explanation of the generous giving.