Found just once in the New Testament (Col. 1:24), the Greek verb “antanapleroo” meant “fill up” or “complete.” Paul said he was “filling up” (completing) Jesus’ sufferings.
Many hated and persecuted Jesus, but all this hate and persecution did not end with Jesus’ death. Followers of Christ have continued to suffer at the hands of unbelievers throughout the Christian era and thus, like Paul, help “fill up” Jesus’ sufferings. Perhaps a good cross-reference is Rom. 8:17.