Charles Spurgeon Commentary 2 Corinthians 8:3

"For according to their power, I bear witness, yea and beyond their power, [they gave] of their own accord," — 2 Corinthians 8:3 (ASV)

For to their power, I bear record, yea, and beyond their power they were willing of themselves;

They were willing to give even beyond their power. They gave up to the full limit of what they could do, and then wished that they could give even more. And notice that "they were willing of themselves." Paul did not have to stir them up to do this, nor even to mention the subject to them: "They were willing of themselves."

That is the best kind of service to God that a man ever does, that in which he is willing of himself. It is the slave who is flogged to his work; the child is willing of himself. Oh, that on the altar of God, you and I may gladly place our offerings because we have been made willing of ourselves!

For to their power, I bear record, yea, and beyond their power they were willing of themselves:

Without any pressure: without even a hint – spontaneously.