From Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother, to the saints, the faithful brothers and sisters in Christ, at Colossae. Grace and peace to you from God our Father! (Colossians 1:1–2 NET)

Did Matthias (Acts 1:26) replace Judas, or was it Paul, the apostle to the gentiles? Luke seems to elevate Paul to the level of the 12 in his 2nd book. Take careful notice of the comparison between Peter and Paul as the book  of Acts progresses; it gives new meaning to the phrase by the will of God. Paul is an apostle, because God made it so.