What, Then, Do I Have To Believe To Be Saved?

The Gospel of John is the ONLY book in the bible whose purpose is to show us how to have eternal life. The purpose statement is found in John 20:31. So the Gospel of John is the place to go if we want to understand what it takes to have eternal life. 
In John, the word “believe” is used about 100 times. John 3:15-18, 3:36, 5:24, 6:28, etc etc. I’m going to pick one. John says over and over that whoever “believes” in Jesus HAS eternal life. Check out the above verses if you want to take a closer look. 
The question then arises, and I think it’s the question everyone needs to ask, “what exactly am I supposed to believe?” This is possibly one of the most important questions we can ask. John 4 and John 11 tell us. Let’s start with John 4:10
Jesus answered and said to her, “If you knew the gift of God, and who it is who says to you, ‘Give Me a drink,’ you would have asked Him, and He would have given you living water.”
This verse shows us that there is a VERY short list of things we MUST believe to have everlasting life, which he calls living water here. 

1. We must know the gift
(eternal life) 
2. We must know who the giver is (Jesus)

Here is a simple phrase to remember this by, “Believe in Jesus for eternal life.” If you’ve believed in Jesus for eternal life then you have it. 
Now let’s look at John 11:25-27. Jesus said to her, “I am the resurrection and the life. He who believes in Me, though he may die, he shall live. And whoever lives and believes in Me shall never die. Do you believe this?” She said to Him, “Yes, Lord, I believe that You are the Christ, the Son of God, who is to come into the world.”
In these verses we see the same idea put into different and non-metaphorical words. Jesus explains that he is the 1. Resurrection and the 2. Life. Once he’s made this statement he asks if Martha believes it, which points to the fact that if someone believe this statement they will be resurrected. This shows us that there are two parts of what we must believe once more. 

1. We must believe the gift (resurrection i.e. Eternal life)
2. the must believe he is the giver (Jesus)

What’s really great about this verse is Martha rephrases Jesus’ words. She encapsulates all of that in this simple phrase, “I believe that you are the Christ, the Son of God, who is to come into the world.” So any time you see someone in scripture come to believe that Jesus is the Christ, it is synonymous with this idea, believe in the gift (resurrection / eternal life) and the giver (Jesus).
So, as John 3:16 and many others tell us, if you believe in Jesus as the giver of eternal life then you have eternal life. It’s really quite awesome. 
So, YES we must believe Jesus was real. We must believe that he will resurrect you to eternal life. If we believe those two things then you have eternal life. 

Believing that Jesus’ teachings are good doesn’t give you eternal life. However, if you believe Jesus’ teachings are good and you obey them, (once you’ve become a believer) He promises to give you extra reward once you get to the Kingdom of Heaven. Matthew 6:19