First, a few testimonies: I have it third hand, that Dr. Howard Hendricks (of Dallas Seminary) once made the statement (and I paraphrase) that if it were his decision, every student graduating from Dallas Theological Seminary would be required to learn one thousand verses word perfect before they graduated.
Dallas Willard, professor of Philosophy at the University of Southern California, wrote, "Bible memorization is absolutely fundamental to spiritual formation. If I had to choose between all the disciplines of the spiritual life, I would choose Bible memorization, because it is a fundamental way of filling our minds with what it needs. This book of the law shall not depart out of your mouth. That's where you need it! How does it get in your mouth? Memorization" ("Spiritual Formation in Christ for the Whole Life and Whole Person" in Vocatio, Vol. 12, no. 2, Spring, 2001, p. 7).
Chuck Swindoll wrote, "I know of no other single practice in the Christian life more rewarding, practically speaking, than memorizing Scripture... No other single exercise pays greater spiritual dividends! Your prayer life will be strengthened. Your witnessing will be sharper and much more effective. Your attitudes and outlook will begin to change. Your mind will become alert and observant. Your confidence and assurance will be enhanced. Your faith will be solidified" (Growing Strong in the Seasons of Life [Grand Rapids: Zondervan, 1994], p. 61).
One of the reasons Martin Luther came to his great discovery in the Bible of justification by faith alone was that in his early years in the Augustinian monastery he was influenced to love Scripture by Johann Staupitz. Luther devoured the Bible in a day when people earned doctorates in theology without even reading the Bible. Luther said that his fellow professor, Andreas Karlstadt, did not even own a Bible when he earned his doctor of theology degree, nor did he until many years later (www.orlutheran.com/html/luthbibl.html). Luther knew so much of the Bible from memory that when the Lord opened his eyes to see the truth of justification in Romans 1:17, he said, "Thereupon I ran through the Scriptures from memory," in order to confirm what he had found.
So here are a few reasons why so many have viewed Scripture memorization as so essential to the Christian life.
1. Conformity to Christ
Paul wrote that "we all... beholding the glory of the Lord, are being transformed into the same image from one degree of glory to another." If we would be changed into Christ likeness we must steadily see him. This happens in the word. "The LORD revealed himself to Samuel at Shiloh by the word of the LORD" (1 Samuel 3:21). Bible memorization has the effect of making our gaze on Jesus to be steadier and clearer.
2. Daily Triumph over Sin
"How can a young man keep his way pure? By guarding it according to your word... I have stored up your word in my heart, that I might not sin against you" (Psalm 119:9, 11). Paul said that we must "by the Spirit... put to death the [sinful] deeds of the body" (Romans 8:13). The one piece of armor used to kill is the "sword of the Spirit," which is the word of God (Ephesians 6:17). As sin lures the body into sinful action, we call to mind a Christ-revealing word of Scripture and slay the temptation with the superior worth and beauty of Christ over what sin offers.
3. Daily Triumph over Satan
When Jesus was tempted by Satan in the wilderness he recited Scripture from memory and put Satan to flight (Matthew 4:1-11).
4. Comfort and Counsel for People You Love
The times when people need you to give them comfort and counsel do not always coincide with the times you have your Bible handy. Not only that, the very word of God spoken spontaneously from your heart has unusual power. Proverbs 25:11 says, "A word fitly spoken is like apples of gold in a setting of silver." That is a beautiful way of saying, When the heart full of God's love can draw on the mind full of God's word, timely blessings flow from the mouth.
5. Communicating the Gospel to Unbelievers
Opportunities to share the gospel come when we do not have the Bible in hand. Actual verses of the Bible have their own penetrating power. And when they come from our heart, as well as from the Book, the witness is given that they are precious enough to learn. We should all be able to sum up the gospel under four main headings (1) God's holiness/law/glory; 2) man's sin/rebellion/disobedience; 3) Christ's death for sinners; 4) the free gift of life by faith. Learn a verse or two relating to each of these, and be ready in season and out of season to share them.
6. Communion with God in the Enjoyment of His Person and Ways
The way we commune with (that is, fellowship with) God is by meditating on his attributes and expressing to him our thanks and admiration and love, and seeking his help in living a life that reflects the value of these attributes. Therefore, storing texts in our minds about God helps us relate to him as he really is. For example, imagine being able to call this to mind through the day:
The LORD is merciful and gracious, slow to anger and abounding in steadfast love. He will not always chide, nor will he keep his anger forever. He does not deal with us according to our sins, nor repay us according to our iniquities. For as high as the heavens are above the earth, so great is his steadfast love toward those who fear him; as far as the east is from the west, so far does he remove our transgressions from us. As a father shows compassion to his children, so the LORD shows compassion to those who fear him. For he knows our frame; he remembers that we are dust. (Psalm 103:8-14)
I used the word "enjoyment" intentionally when I said, "communion with God in the enjoyment of his person and ways." Most of us are emotionally crippled -- all of us really. We do not experience God in the fullness of our emotional potential. How will that change? One way is to memorize the emotional expressions of the Bible and speak them to the Lord and to each other until they become part of who we are. For example, in Psalm 103:1, we say, "Bless the LORD, O my soul, and all that is within me, bless his holy name!" That is not a natural expression for many people. But if we memorize this and other emotional expressions from the Bible, and say them often, asking the Lord to make the emotion real in our hearts, we can actually grow into that emotion and expression. It will become part of who we are. We will be less crippled emotionally and more able to render proper praise and thanks to God.
There are other reasons for memorizing Scripture. I hope you find them in the actual practice.