At CE, we love the Bible because it is the inspired word of God. It's not just an add-on to becoming a disciple. It is vital. The Bible is not some instruction manual on how to live a good Christian life, it is a book that gives life:
It Convicts you of your Sin: The bible is the instrument that God through the Holy Spirit uses to convict you of your sin. See John 16:8, Ephesians 6:17 and Hebrews 4:12.
It Shows the Way: The bible is involved when someone comes to faith, whether is it through powerful preaching from God's word or simply reading some of the Gospels. It is the book God uses to bring people into a relationship with Jesus Christ. To show people how to receive forgiveness from their Sin. See it described in Psalm 119:59-60, illustrated in Luke 15:11-24, and described again in 2 Corinthians 5:17.
It Comforts the Disciple: The bible is one of the ways God brings comfort to people of the Kingdom in times of suffering. God's word gives solid spiritual comfort that gives us wisdom, during the daily realities of life. It is the comfort and truths, found in scripture that spur us to live for God, serve him and if necessary suffer, so he is glorified. See Psalm 119:165; Isaiah 41:10; Psalms 23, 27, 34, 91; John 14:1-3 or Philippians 4:19.
It Reveals our King: The bible is all about Jesus, it is the sole revelation we have of Christ and God's plan for salvation. Consider the Emmaus Road experience, when two unnamed disciples are heading out of Jerusalem just after the crucifixion and are unaware of the resurrection. Jesus joins them and seeks to understand their sadness, then "beginning with Moses and all the Prophets, he explained to them what was said in all the Scriptures concerning himself." Jesus used all of scripture to reveal himself (Luke 24:13-27). So both the Old Testament and New Testament are vital to the Christian in knowing more of Jesus and becoming more like him. Jesus is the word of God. (John 1)