31 What that is must be understood in view of this same hope of our faith. We cannot be ignorant that the Lord Jesus Christ rose again from the dead, and sits at the right hand of God, for we have also the witness of the Apostle, According to the working of the strength of His might, which He wrought in Christ, when He raised Him from the dead, and made Him to sit at His right hand in the heavenly places above all rule and authority and power and dominion, and every name that is named not only in this world but also in that which is to came, and put all things in subjection under His feet. The language of the Apostle, as befits the power of God, speaks of the future as already past: for that which is to be wrought by the completion of time already exists in Christ, in Whom is all fullness, and 'future' refers only to the temporal order of the Dispensation, not to a new development.
Thus, God has put all things under His feet, though they are still to be subjected. By their subjection, conceived as already past, is expressed the immutable power of Christ: by their subjection, as future, is signified their consummation at the end of the ages as the result of the fullness of time.
Source: On the Trinity (New Advent)