This is one of the most triumphant of the traditional Christmas hymns, deserving an equally jubilant (joyful, loud) registrational treatment. This three-part arrangement carries the hymn melody in normal note values in the higher manual part, an equally active lower manual part, and a bass line in the normal range played in the pedal. We should register both manual parts on the usual 8' foundation, and the pedal on its traditional 16' foundation.
The first part seems to call for a solo trumpet, supported by firm flue choruses in the other two parts. If the solo 8' trumpet is not strong enough, try a full reed chorus (chorus reeds 16', 8', and 4') with the mixture or with the other principal chorus members. Reeds can also be supported by fifth- and third-sounding mutations. Lacking a good reed foundation for the first part, try using the main principal chorus, supported by less assertive foundations in the other parts.