As a banker he naturally became a PCC treasurer, and had to review an ordinand's budget. He wanted to speak from the experience of what this has meant for himself. It is purely a matter of grace. Proportional giving is vital. It is not how much you get.
Experience is that it is the poorer people and the clergy who are the most generous.
Giving is blessed by God, but not necessarily in money. It's not a bargain with God. A generous businessman became penniless. But he said 'I still possess the money I gave to God', he couldn't lose that. Time, talents and money go together in discipleship.