 He's reminding them that they are sealed by the Holy Spirit of God until the day that Christ returns to take them to heaven. But that's not the filling of the Holy Spirit. The sealing of the Holy Spirit in Ephesians chapter 113 is different from the filling of the Holy Spirit. There are two different things. You are sealed with the Holy Spirit the moment you believe in the Lord Jesus Christ. But you are told in Ephesians 5.18 to be filled with the Holy Spirit.