It's incredible to think that Peter was not a single guy when he was following Jesus all over creation, but a married man with responsibilities at home. Sometimes we get the idea from Peter's example that the mark of true discipleship is the extent to which you can abandon and neglect your family responsibilities ("Behold, we have left everything and followed you"), and yet here we glimpse a different side of the story. Peter had evidently not neglected his family but had even taken his ailing mother-in-law into his home. What's more, Peter shows that being Jesus' disciple doesn't always mean taking your relationship with him away from the home to some exciting new place. Instead it means bringing Jesus into your own home where you introduce him to your family members, where he can touch them with his healing power and make disciples of them too.
Jesus sees Peter's mother-in-law lying sick in bed with a fever. Some commentators think she may have had malaria, which would explain Jesus' concern for her. No special request for her healing is made. In fact, you get the impression that Jesus heals her simply because she belongs to Peter's household, that his relationship with Peter naturally overflows into blessing everyone dear to Peter. It goes to show that if you're a Christian, there's a sense in which everyone you care about is automatically on Jesus' radar screen too, since Jesus' love is so intertwined with your own.
Jesus touches her hand and the fever leaves her. Immediately she rises and begins to serve him. If she wasn't a disciple before, she is now. Serving Jesus is the fundamental mark of discipleship, and Peter's mother-in-law's response of service immediately after her healing nicely sums up the Christian life. Once you were in bondage to sin and death, but the moment you were reborn through Jesus' healing touch you became his bondservant. No service you give can repay him for his gift of life, rather you render it out of love and gratitude. It is because you can't repay Jesus that you serve him so diligently.
There's a part of us that may be tempted to overlook this detail of Peter's mother-in-law's service. Culturally speaking, a senior female member of the household might be expected to wait upon a guest in her home, especially a guest who had just done her a great service. There may even be a sexist part of us that figures it is simply her job as a woman to serve a male guest, especially someone like Jesus who carries the status of a rabbi. But even if her response can be partly explained as "cultural" or as "a woman's job," it's interesting to see that the Gospel writer still takes note of her service through the Holy Spirit's inspiration. No doubt Jesus recognizes the love and gratitude that motivates her response, and he would not discount her service simply because she is also under a cultural and social obligation to render it.
In our modern feminist culture I think a lot of us women are made to feel that there are only two ways to live: either give in to patriarchal expectations about women's roles and be enslaved to the male authorities in your life; or be free of such expectations, take charge of your own life and live as you please. Yet it is an inescapable fact that the most obvious and practical way for a Christian woman to serve Jesus is through serving other people--and quite often those people will be overbearing male authorities. But just because you might take on the appearance of being a woman who is still "backward" and "traditional" ("She probably has low self-esteem, the poor, uneducated thing"), if your real motivation is serving Jesus, you can be sure that he will not misread your actions. He won't despise you as unenlightened and unliberated because you quietly serve a selfish and demanding husband, father or boss, but will recognize your service as being done solely out of devotion to him.