Adam Clarke on 1 Corinthians 15:10

But, by the grace of God I am what I am - God, by his mere grace and good will, has called me to be an apostle, and has denominated me such.

And his grace, etc. - Nor have I been unfaithful to the Divine call; I used the grace which he gave me; and when my labors, travels, and sufferings are considered, it will be evident that I have labored more abundantly than the whole twelve. This was most literally true.

Yet not I, but the grace of God - It was not through my own power or wisdom that I performed these things, but through the Divine influence which accompanied me.