Paul's authority

Paul talks first about his apostleship and next he speaks of his authority in Romans 1:5," through whom we have received grace and apostleship to bring about obedience of faith for the sake of his name among all the nations."
Paul had nothing by which to commend himself to God. Rather, God poured out apostleship by grace upon him. Any authority he had as an apostle had come by grace from God and had been validated by Paul's own obedience.