Jesus cast out many demons right after healing Peter’s mother-in-law, because her liberation and healing was a further sign of Jesus’ power, encouraging others to seek his help, which he exercised at night (Matthew 8:16) and in a home as powerfully as during the day in a synagogue (Mark 1:23–27).
Matthew 8:16 highlights the fact that Jesus has complete power over demons. As their sovereign Lord he casts them out with a single command. Furthermore, the text highlights that he not only healed a select few, but all who were in a bad way as a result of demon oppression. His therapy is infallible; the results are comprehensive. By virtue of this sequel to the healing of Peter’s mother-in-law, she becomes a sign and symbol of Jesus’ boundless power over demons, not only at home but everywhere, and not only during the day but also at night. We can therefore take courage from the fact that her healing was not an exception, but rather a model.1
16 That evening they brought to him many who were oppressed by demons, and he cast out the spirits with a word and healed all who were sick.