Weak in Him But Powerful by God

2 Corinthians 13:4 KJV
For though he was crucified through weakness, yet he liveth by the power of God. For we also are weak in him, but we shall live with him by the power of God toward you.

Paul was not afraid to be weak in the flesh. He was a humble man and gladly accepted the humbling of himself and the belittling of his own reputation.

But Paul was also not afraid to demonstrate the power of God toward people. And it appears this was something he could choose to do. He would rather not use sharpness but was capable of it and willing to do it when it became necessary.

A man of God is a weak man.
He knows his limitations.
He acknowledges his sins.
He senses the battle in his own soul.
He witnesses those who refuse to accept his message.
But he is not a weakling and those would think that of him had better take note. He has an authority of God that he may rightfully use.
An authority to rebuke
An authority to be sharp
An authority to exercise "the power of God" toward those who will not be right with God.
And he has every right to demonstrate that power without guilt; regardless of the response of those, he as demonstrated it toward.