Paul preaches Christ crucified. He tells the story of Jesus dying to save sinners. He offers Christ to everyone who will receive him as the power and the wisdom of God. So in one crucial sense Paul and God are calling all people to take Christ into their lives as power and wisdom. When we do, the same thing happens that happened when Paul preached.
Some listeners stumble over the gospel as unacceptable.
Some say it is foolishness. And they believe and are saved. In other words, the preaching of the gospel is not exactly the same as the call of God. All the Jews and Greeks were hearing the preaching of the gospel. But some were rejecting it.