In Matthew 25:40 (in the parable of the sheep and the goats), The Lord says: "...Truly I tell you, whatever you did for one of the least of these brothers and sisters of mine, you did for me."
This verse speaks of the deep of love of God for even the least of his subjects. I love my mother very much. I feel indebted to anyone who extends a helping hand to her in her old age. For example, I feel indebted to my niece who regularly makes sure she has the right medicine. The more we love a person, the more we are touched when another person shows kindness to our loved one.
Everyone should always show kindness, respect, and love to his or her spouse's parent. In this way, he or she will touch the heart and earn the gratitude and indebtedness of the spouse. Well-brought up children learn this from young. I stopped at a coffee shop yesterday and ordered a coffee. After I was billed, I asked the person about his father (he didn't know me), and immediately he insisted on giving me discount on the coffee. The young man left a positive impression on me. Even though he did not know me, he did for me what his father would have done.