For this I was appointed a preacher and an apostle (I am telling the truth, I am not lying) as a teacher of the Gentiles in faith and truth.Paul here is reminding both Timothy and the readers/hearers of this letter that he was appointed for three specific works by Christ on the road to Damascus. He was to be 1) a Preacher, 2) an Apostle, and 3) a Teacher of the Gentiles. Now to be sure while these offices are interrelated for Paul they are significantly different for Paul's ministry imparticular. For one Paul derives his authority to preach the Gospel from where? His time with Prof. Gamaliel, graduation from Jerusalem Theological Seminary, and ordination by the Presbytery of Tarsus? No! Paul receives his authority to preach from Jesus Christ himself!!! Paul is a full apostle with the same rights and privileges of the 12 Apostles present at Pentecost. This is vitally important when reading Paul's letters and listening to those who challenge Paul's authority, both at the Jerusalem Council in Acts 15 and today when "Professors" dismiss Paul's "personal thoughts" as mere opinion and conjecture which has no more weight than my own discretion. This is bubkus pure and simple. Who are we to challenge the words of an Apostle sent by Christ himself? Well simply to put it in words a 3rd grader could understand, Paul is an Apostle and we are not so it may be a good idea to listen to the Apostle's "opinion" and not our own.
Also worth thinking about is Paul's use of the word "this". For what is it that Paul has been appointed to teach and preach? To use Paul's own words in 1st Corinthians 15:1-19:
Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand, by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain. For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures, and that He appeared to Cephas, then to the twelve. After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep; then He appeared to James, then to all the apostles; and last of all, as to one untimely born, He appeared to me also. For I am the least of the apostles, and not fit to be called an apostle, because I persecuted the church of God. But by the grace of God I am what I am, and His grace toward me did not prove vain; but I labored even more than all of them, yet not I, but the grace of God with me. Whether then it was I or they, so we preach and so you believed. Now if Christ is preached, that He has been raised from the dead, how do some among you say that there is no resurrection of the dead. But if there is no resurrection of the dead, not even Christ has been raised; and if Christ has not been raised, then our preaching is vain, your faith also is vain. Moreover we are even found to be false witnesses of God, because we testified against God that He raised Christ, whom He did not raise, if in fact the dead are not raised. For if the dead are not raised, not even Christ has been raised and if Christ has not been raised, your faith is worthless; you are still in your sins. Then those also who have fallen asleep in Christ have perished. If we have hoped in Christ in this life only, we are of all men most to be pitied.