How do we know that God calls certain people to preach the gospel?

The evidence of God's calling to preach is found in their understanding of the gospel and their position as unprofitable servants, as highlighted in Luke 10:1-16. Those appointed do not preach a gospel that relies on human will or merit but proclaim the truth of God's grace that excludes human boasting. The distinction is clear: preachers are chosen by God, and they recognize their duty to proclaim Christ's glory. This aligns with the doctrine of God's sovereign election, supporting the assertion that it is God alone who equips and sends his messengers to share the gospel, thus inviting His people to Himself.