Psalm 119:10–12 (ESV): "10 With my whole heart I seek you; let me not wander from your commandments! 11 I have stored up your word in my heart, that I might not sin against you. 12 Blessed are you, O Lord; teach me your statutes!"
The Word of God is pure light and it exposes everything that resides in darkness. Sin can't hide from it thus memorizing the Word becomes a powerful means of battling sin in the life of a believer.
David begins this psalm by making a declaration about those who are "happy" in the Lord. He says blessed are those who walk in and keep the Lord's commands. The reason we are "happy" when we are walking in obedience to His Word is because God's Word is pure light and it exposes the path of God's best for us. If we hide His Word in our hearts it will direct us to the place of blessedness. It's our guide to true and lasting contentment. Jesus told us part of the Great Commission was to teach people to observe all that He commanded us (Matt 28:20) because it is the only way to be truly "happy" in this life.
The memorization of Scripture is important to the life of a believer because it exposes the deception of sin. You can't avoid what you don't see or know. God wants us to live in liberty and freedom and this is found only in walking out His Word. Seek the Lord wholeheartedly through His Word and hide it in your heart and you will be amazed at how truly blessed you will be.
Father, thank You for Your Word. It is useful for teaching, reproofing, correcting, and training in righteousness, that the man of God be complete, equipped for every good work (2 Tim 3:16). Help us to know and obey Your Word. It is a tool You use to lead us to the blessed state of contentment. Give us a strong desire to know Your Word. Thank You for Jesus who paid the price for our sin and who is the Word made flesh. May we walk in His ways we pray in Jesus' name, amen.