Eph 2:8,9 (NIV) 
For it is by grace you have been saved, through faith--and this is not from yourselves, it is a gift of God--not by works, so that no one can boast. 
How is a person made right with God? Before the Reformation, the main belief was that a person could gain forgiveness of sins and heaven through performance of good works, and holy acts of pure devotion to God. Most people were uncertain that they had done enough to please God and felt their eternal salvation was in question. Martin Luther was among those who questioned their qualification for heaven. In those days most people did not have access to Bibles and could not read and study it for themselves. They had to depend on what they were told by church authorities. They were not always told the truth. Even most priests were ignorant of what the Bible taught.  
Martin Luther had become a priest. He was also appointed a university professor to teach the Bible. Through his careful study he discovered the simple truth that a person is not saved by human effort, but by God's grace [undeserved favor or love] as a gift. This grace was demonstrated in the perfect life, the sacrificial death, and the triumphant resurrection of Jesus Christ. 
Rom 3:22-25 (NIV) There is no difference, for all have sinned and fall short of the glory of God, and are justified by his grace through the redemption that came by Christ Jesus. God presented him as a sacrifice of atonement, through faith in his blood.  Luther later reflected that when this discovery came to him, it was as though "the gates of paradise swung open before me and I was born anew." 
Rom 5:1 (NIV) Therefore, since we have been justified through faith, we have peace with God through our Lord Jesus Christ.  
Acts 16:31 (NIV) They replied, "Believe in the Lord Jesus, and you will be saved--you and your household." Also in contrast to works or human effort, a person is saved by God's grace through faith. Faith is simply like the hand which receives and embraces the offered gift. Faith accesses the promised gifts and blessings of God. Faith is made possible in the human heart by the power of the Holy Spirit. 
John 5:24 (NIV) "I tell you the truth, whoever hears my words and believes him who sent me has eternal life and will not be condemned; he has crossed over from death to life." 
The Bible is the authority given to us by God to establish doctrine and to guide us in our daily living. Human religious writings and authorities are valid only when they accurately reflect and teach what Scripture does. Careful reading and scholarship can help us understand God's intended meaning of the Bible, but only the Holy Spirit, working through the Word, can bring us to truly know God and accept his plan of eternal life for us. The central message of the Bible is Jesus Christ, and its central purpose is to bring us to faith in Him. The entire Bible is inspired by the Holy Spirit and is completely truthful and reliable. 
Prov 30:5 (NIV) "Every word of God is flawless; he is a shield to those who take refuge in him" 
John 20:31 (NIV) But these are written that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.