Paul's enigmatic claim in Col 1:24 that “he completes what is lacking with regard to the sufferings of the Messiah” has puzzled exegetes for centuries. Lexicographical analysis of the verb άνταναπληρόω has established its meaning as “to complete in the place of another,” a sense that rules out the most popular explanations. A new interpretation is proposed that begins by recognizing that Paul makes this statement with reference to his calling to be the apostle to the Gentiles. An examination of other relevant Pauline texts reveals that he finds the theological basis for his unique apostolic ministry in Isaianic Servant traditions, especially the second Servant Song. It is argued that, since Paul believes he has been given a role in completing the Servant's mission to be a light to the nations (compare Acts 13:47 with Isa 49:6), he may well have sensed a calling to complete the Servant's sufferings as described in the fourth Servant Song.