A.T. Robertson Commentary 2 Corinthians 4:13

"But having the same spirit of faith, according to that which is written, I believed, and therefore did I speak; we also believe, and therefore also we speak;" — 2 Corinthians 4:13 (ASV)

According to that which is written (κατα το γεγραμμενον). This formula in legal documents in the papyri (Bible Studies, p. 250). Paul makes adaptation of the words in Ps 95:1.

We also believe (κα ημεις πιστευομεν). Like the Psalmist. And therefore can speak with effect. Otherwise useless.

Shall present us with you (κα παραστησε συν ημιν). This shows that Paul was not certain that he would be alive when Jesus comes as has been wrongly inferred from 1 Corinthians 7:29; 10:11; 15:51.