In a general sense it can be said that the Bible was written to convict sinners of sin and to equip believers for service.

1. It equips for evangelism.  Philip uses the 53rd Chapter of Isaiah to point the Ethiopian eunuch to Christ in Acts 8:26-39 "And the angel of the Lord spake unto Philip, saying, Arise, and go toward the south unto the way that goes down from Jerusalem unto Gaza, which is desert. And he arose and went: and, behold, a man of Ethiopia, an eunuch of great authority under Cadace queen of Ethiopians, who had the charge of all her treasure, and had come to Jerusalem for to worship, was returning, and sitting in his chariot read Esaias, and said, Do you understand what you read? And he said, How can I, except some man should guide me?  And he desired Philip to come up and sit with him.  The place of the scripture which he read was this, He was led as a sheep to the slaughter; and like a lamb dumb before his shearer, so opened not he his mouth:  In his humiliation his judjment was taken away, and who shall declare his generation? for his life is taken from the earth.  And the eunuch answered Philip, and said, I pray thee, of whom speaks the prophet this? of himself? or of some other man?  Then Philip opened his mouth, and began at the same scripture, and preached unto him Jesus.  And as they went on their way, they came unto a certain water; and the eunuch said, See, here is the water; what does hinder me to be baptized?  And Philip said, If you believe with all your heart, you may.  And he answered and said , I believe that Jesus Christ is the Son of God.  And he commanded the chariot to stand still:  and they went down both into the water, both Philip and the eunuch; and he baptized him.  And when they came up out of the water, the Spirit of the Lord caught away Philip, that the eunuch saw him no more; and he went on his way rejoicing.

2.  It equips for counseling others.  In his two letters to Timothy, Paul constantly urges this young man to preach the Word of God.  1 Timothy 1:3, 18; 4:13-15; 2 Timothy 2:1, 2, 15. 

As I besought you to abide still at Ephesus, when I went into Macedonia, that you might charge some that they teach no other doctrine.  This charge I commit unto you, son Timothy, according to the prophecies which went before on you, that  y ou by them might war a good warfare.  Till I come, give attention to reading, to exhortation, to doctrine.  Neglect not the gift that is in you, which was given you by prophecy, with the laying on of hands of the presbytery.  Meditate upon these things; give yourself wholly to them; that your profitiny may appear to all. 

 You therefore, my son, be strong in the grace that is in Christ Jesus.  And the things that you have heard of me among many witnesses, the same commit you to faithful men, who shall be able to teach others also.  Study to show yourself approved unto God, a workman that need not be ashamed, rightly dividing the word of truth.

"If you put your brother in rememberance of these things, you shall be a good minister of Jesus Christ nourished up in the words of faith and of good doctrine, whereunto you have attained." 1 Timothy 4:6

3. It equips for using one's spiritual gifts from God.  A spiritual gift is an ability given by the Holy Spirit to the believer for the purpose of edifying the church and gloryfying God.  In Ephesians 1:17-19 and 4:7, 11-14 Paul says the knowledge of God's Word will provide with the maturity we need to use our gifts in the most effective way. 

Ephesians 1:17-19  That the God of our Lord Jesus Christ the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him: The eyes of your understanding being enlightened; that you may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints, And what is the exceeding greatness of his power  to  them who believe, according to the working of his might power.  4: 7, 11-14  But unto every one of us is given grace according to the measure of the gift of Christ.  And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers:  For the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ,  Till we all come in the unity of the faith, and the Knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:  That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive;

4.  It equips us for doing battle with Satan.  In Ephesians 5:10-17 Paul likens the believer's armor to that used by Roman foot soldiers.  "Proving what is acceptable unto the Lord.  And have no fellowship with the unfruitful works of darkness, but rather reprove them.  For it is a shame even to speak of those things which are done of them in secret.  But all things that are reproved are made manifest by the light: for whatsoever doth make manifest is light.  Wherefore he said, awake you that sleep, and arise from the dead, and Christ shall give you light.  See then that you walk circumspectly, and not as fools, but as wise, Redeeming the time, because the days are evil.  Wherefore be you not unwise, but understanding what the will of the Lord is.

In this comparison the Word of God is likened to the soldier's sword.  In a general sense it can be said that the Bible was written  to convict sinners of sin and to equip believers for service.