John 20:31
31 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.
According to the NIV study note, The writer's purpose was to draw them to belief in Christ; he uses the verb "believe" 98 times. In all the gospels and in all letters, you hear a lot of about belief. It must be pretty important to God that we believe that Jesus is the Christ.
God tells us in John 3:16:
"For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life." God loves us and sent his Son to die for our sins. Sin separated us from him. By sending his Son, he atoned for our sins. In other words, we no longer have to be punished for our sins. We are no longer separated from God.
But it is our choice to believe. He won't force it on us. He lets us know that by believing, we get to be in connection with him again. We will spend eternity with him. He gives us the gift of eternal life. He also gives us this gift in John 1:12: Yet to all who received him, to those who believed in his name, he gave the right to become children of God. Think about that! By believing in him, we get to become God's children! All he asks, is that we believe.
God knew we would struggle with belief at times. So, the NIV note on John 20:31 says that some manuscripts have: But these are written that you MAY CONTINUE to believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name. So, if you are struggling with unbelief because of your current circumstances, reading the scriptures will help you believe again.