Throughout the movie, he refers to polaroid photographs with hastily written messages. He has tattoos all over his body to remind him of who he is, what he is looking for, and other pertinent information about the people whom he meets while trying to track down the person who killed his wife.
Towards the end of the movie, even his long-term memories begin to mesh and become distorted with other memories. One frequent character interrupts his flow of reasoning and recollection with the different nicknames that he has acquired and has used to describe himself.
At the end of the movie, the main character tells himself, "I have to believe that there is a world outside of my mind," whereupon he writes a false message for himself to target the wrong man for the murder of his wife.
When human beings attempt to define themselves and their mission in life, they inevitably find their identity and initiative convulted and mired in mistakes and mishaps. Much of the time, our emotions frustrate our constancy, our resolve gives way to momentary distractions. Sometimes, we find ourselves weighed down by the empthy thoughts and actions of years past. Man simply cannot rely on his own memory, his own thoughts, his varied and vicarious feelings to steel himself through life and style himself to his felllow man.
For the believer, he does not have to resort to such flimsy and unreliable methods to protect his identity, to establish himself. He has theh Word of God, Christ Jesus, the Second Person of the Holy Trinity:
"In the beginning was the Word. And the Word was with God; and the Word was God." (John 1: 1)
In the Old Testament, the Law and the Prophets witness to the power and purpose of the Word of God in our lives:
"And he [The LORD] humbled thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that he might make thee know that man doth not live by bread only, but by every word that proceedeth out of the mouth of the LORD doth man live." (Deuteronomy 8: 3)
"LAMED. For ever, O LORD, thy word is settled in heaven." (Psalm 119: 89)
"The grass withereth, the flower fadeth: but the word of our God shall stand for ever." (Isaiah 40: 8)
"So shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall accomplish that which I please, and it shall prosper in the thing whereto I sent it." (Isaiah 55: 11)
Not man's utterances, or even the futile sounds of nature, but the Word of God, which made the worlds, the universe, everything that is. This same Word supplies us everything that we need, everything that we are:
"But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God." (Matthew 4: 4)
"Heaven and earth shall pass away, but my words shall not pass away." (Matthew 24: 35)
The Word of God is everlasting, the source of eternal constancy that every man craves and cannot find in anything else:
"But the word of the Lord endureth for ever. And this is the word which by the gospel is preached unto you." (1 Peter 1: 25)
This is our identity, found in the Word of God, in Christ Jesus, for as the Apostle John wrote in his first epistle:
"Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.
"And every man that hath this hope in him purifieth himself, even as he is pure." (1 John 3: 2-3)
"Herein is our love made perfect, that we may have boldness in the day of judgment: because as he is, so are we in this world." (1 John 4: 17)
We sit in high places with Christ Jesus (Ephesians 2: 6), He is within us, our hope of glory (Colossians 1: 27). He is our bread and water (John 6: 35); He is our Way in a dark world; He is the Truth for unsettled mind and despairing spirits, He is the Life for a defeated and alienated people (John 14:6)
The Word of God lives in every believer:
"Let the word of Christ dwell in you richly in all wisdom; teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord." (Colossians 3: 16)
Unlike the main character in "Memento", if a believer finds himself lost, confused, unsure as to what he must do, by meditating on the Word of God, by communing with God, letting the Word of God settle in our hearts, we are transformed from glory to glory, we become more like Him who loved us and died for us, we realize ever more that we are more like Him. We never need to wonder who we are, no matter how dark, dank, and dangerous the world may become for us. No matter how bad we may feel, no matter how distant our thoughts may be from the glorious ideal, who we are in Christ will never change, He will never leave us nor forsake us, and nothing can separate us from His love, not our sin, not or sorrow, not any shame from the past, present, or future!