Paul Kneels in Prayer in the Arabian Desertby emmanuel_higgins

Galatians 1:15

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

Paul's apostleship and his mission to the Gentiles came from God by grace and by God's will, not from human choice or human appointment. God separated him and called him by grace and appointed him to that work, and his calling to be an apostle rested on God's grace and power. His conversion turned him from persecuting unbelief to faith in Jesus, when an encounter with divine glory first brought terror and then consolation, and transforming mercy made him a penitent and fervent believer.

The verse belongs to his account of his conversion and early Christian experience, which shows that divine power led him to understand the truths of the gospel. Christ was revealed to him, and his instruction came directly from God and from Christ rather than from human teachers or instruction by people. His preaching therefore did not come from men, but from God leading him into the gospel he was to proclaim.

To prepare for that work he went to Arabia to seek God, to deepen his repentance, and to get ready through prayer and study. Jesus strengthened his faith there and assured him of sustaining grace for the mission ahead. He continued that preparation through prayer and communion with Christ, who strengthened him and gave him wisdom and grace. In response to this calling he gave up the honors and advantages he could have pursued and devoted his life to preaching Christ, not for worldly or selfish gain.