Very truly I tell you, anyone who hears my word and believes Him who sent me has eternal life and does not come under judgement, but has passed from death to life. (John 5 v 24)
Remember the rich man in the Bible who asks Jesus what he must do to be saved? Jesus tells him to follow the ten commandments, and then to go and give all his wealth away and follow Him. He couldn't do the second part.
The " believing" in Jesus in the verse above is the easy part - most of us would say that Jesus did exist, and some of us would go one step further, and say that they believe He is the Son of God. "Box ticked" on the way to eternal life! But what about the "hearing my word" part? Jesus came to turn the world upside down with his radical teachings - forgive those who have hurt you, love those you don't even like (!). Following Jesus means to do as He did when He was on the earth. Follow His example in our treatment of others. Yes, we will get it wrong - our human nature will often win out, over our God given nature, but God is interested in the motivation of our hearts, and the more we try to follow Jesus' example, the closer we come to eternal life - a life lived with God in love, peace and joy. This life is like a drop in the ocean, compared to the life still to come. That's what we need to be working towards.