Joshua 4:24 (KJV) That all the people of the earth might know the hand of the LORD, that it is mighty: that ye might fear the LORD your God for ever.
Sometimes Christ will work in our lives as a witness to other people. Not just what we call blessings, but also the trials and hardships. People around us see what is going on and how we get through it as a testimony to the goodness of Jesus Christ. Also as time goes on the memory fades and we need a memorial as a reminder of what we have overcome.
Think about all of the historical sites that we have with some sort of memorial building, statues, or some sort of wall with the names of heroes. These give us an opportunity to reflect on our past and consider our future.