Ephesians 3:8

Paul considered himself the least worthy (lit. the "leaster") of all the saints (Ephesians 1:1) to have received such a privilege. This unusual expression is "a comparative of the superlative." [Note: Martin, p. 1308.] Rather than thinking God owed him something, Paul regarded God’s entrusting him with the gospel as pure grace, unmerited favor (cf. 2 Corinthians 12:11).

"Perhaps he was deliberately playing on the meaning of his name. For his Roman surname ’Paulus’ is Latin for ’little’ or ’small’, and tradition says he was a little man. ’I am little,’ he may be saying, ’little by name, little in stature, and morally and spiritually littler than the littlest of all Christians.’" [Note: Stott, p. 119.]

The unfathomable riches of Christ are what Paul preached and what he expounded in this epistle particularly (cf. Romans 11:33).