It is a trustworthy statement, deserving full acceptance, that Christ Jesus came into the world to save sinners, among whom I am foremost of all. (1 Timothy 1:15)
Yet for this reason I found mercy, so that in me as the foremost, Jesus Christ might demonstrate His perfect patience as an example for those who would believe in Him for eternal life. (1 Tim 1:16)
Now to the King eternal, immortal, invisible, the only God, be honor and glory forever and ever. Amen. (1 Tim 1:17)
These passages from 1 Timothy were written by Paul, a man who once persecuted Christian men, women, and children. Paul never forgot what he once was, but neither did he dwell on it. When he mentioned it at all, it was because he wanted to bring glory to Jesus Christ.
The Lord used Paul powerfully. Consider how much of the New Testament was written by this former “persecutor of the church.” (Philippians 3:6)
Yet, as William MacDonald observes, “This man who had learned to be content with whatever material things he had never could be content with his spiritual attainments. He did not count himself to have ‘arrived,’ as we would say today.”
Paul never stopped serving Christ.
Brethren, I do not regard myself as having laid hold of it yet; but one thing I do: forgetting what lies behind and reaching forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus. (Philippians 3:13-14)
MacDonald writes that Paul, “was a man of single purpose. He had one aim and ambition. In this he resembled David, who said, ‘One thing have I desired of the Lord.’ Forgetting those things which are behind would mean not only his sins and failures but also his natural privileges, attainments, and successes…and even his spiritual triumphs.” 
There is much to be thankful for: How the Lord has rescued us; the lives He has given us; the honor of serving Him. We who know Him as Lord and Savior need not fear the future.
Oh give thanks to the LORD, for He is good, For His lovingkindness is everlasting. (Psalm 107:1)
Let the peace of Christ rule in your hearts, to which indeed you were called in one body; and be thankful. (Colossians 3:15)
1. William MacDonald, Believer’s Bible Commentary, p. 1975