Why did God set Paul apart and call him by grace?

God set Paul apart and called him by grace to reveal His Son in him, that he might preach Him among the heathen Gentiles. God deliberately kept Paul from the twelve apostles and sent him to Arabia to receive revelations directly from the ascended Lord for the Gentile world.

Les teaches that God separated Paul from his mother's womb and called him by grace to reveal His Son in him, so Paul could preach Him among the heathen Gentiles. God deliberately kept Paul from the twelve apostles, sending him instead to Mount Sinai in Arabia for three years to receive revelations directly from the Ascended Lord. Had Paul gone back to Jerusalem, the twelve would have drummed into him that Jesus was Israel's Messiah and King, still willing to be King if Israel repented. But God wanted Paul to learn these things from His own heavenly position and take that message to the Gentile world.

Galatians 1:15

But when it pleased God, who separated me from my mother’s womb, and called me by his grace,

Galatians 1:16

To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood:

To whom was Paul called to preach God's Son?

Paul was called to preach God's Son among the Gentiles, also called the heathen. The passage says the revelation was in him so that he might preach Christ among the Gentiles, not so much among the Jews. This commission centered on the Gentile world.