We have to consider 2 Corinthians chapters 8 and 9 together to get the full message St Paul has for us. The generosity he expects from the Corinthians is grounded in the emptying of Christ to which he has referred at 8:9 (and which we find also at Philippians 2:5-11). This movement beyond ego and selfishness is to be the reason for the generosity of the Corinthians, and it will eventually redound to the glory of God.