“Paul, an apostle of Christ Jesus through the will of God, and Timothy our brother,”
Paul starts his letter with his spiritual credentials. Paul does not boast about his academic qualities or qualifications, but values his Apostleship above all. He is an Apostle of Jesus Christ, one born out of time and through the will of God.
He includes Timothy his beloved younger brother, who he has trained up in the ministry and is dependable and faithful to the Lord. The Colossians knew Timothy, and this would add weight to the Epistle and encourage them to listen to what the Apostle said them for their spiritual benefit.
The believers at Colosse had never seen Paul in the flesh and therefore he endears himself to them, that they might listen to the Apostle that God has provided for them, to encourage them in the Lord their God and in their faith in the Lord Jesus Christ.
Paul has the weight of the will and authority of God behind what he is saying here in this letter, and has been made an Apostle and is validated by the Word of God, which he preaches and teaches. All his authority, doctrine and miracles of validation come from God and are validated in the Holy Scripture.