Paul is using himself as an example here. This truth is valid for all though. We may not be like the original apostles, but God has changed each one of us from what we were. It’s through His grace we accomplish anything at all, even just waking up in the morning.
But whatever I am now, it is all because God poured out his special favor on me—and not without results. For I have worked harder than any of the other apostles; yet it was not I but God who was working through me by his grace.
1 Corinthians 15:10 NLT