Why did Paul write the Epistle to Titus?

Titus is a personal letter to a young Gentile man of the same name (whom Paul had led to Christianity) for the purpose of assisting him in the establishment of the new church at Crete. Titus had previously assisted Paul in Corinth.

Titus 1:4

To Titus, mine own son after the common faith: Grace, mercy, and peace, from God the Father and the Lord Jesus Christ our Saviour.