Submit to one another: The verb form connects it with the command to be filled (5:18). This general instruction (compare Philippians 2:3) applies to all three relationships Paul discusses:
wives and husbands (Ephesians 5:22–33),
children and parents (6:1–4), and
slaves and masters (6:5–9).
Believers express submission not out of fear or personal gain, but out of respect for Christ.