"Only give heed to yourself and keep your soul diligently, so that you do not forget the things which your eyes have seen and they do not depart from your heart all the days of your life; but make them known to your sons and your grandsons." (Deuteronomy 4:9)
It helps so much to be reminded of what the Lord has done in our lives. When we're going through a tough time or struggle it can really be encouraging. The Israelites would build stone monuments at places where important events happened. They were visual reminders of what the Lord has done.