Believe! Believe in Jesus. That's the heart of the Gospel...right? But what does it mean to believe in Jesus? I think the Amplified Version of the Bible helps. The Amplified version takes the original Greek language and tries to find more than one word to help us understand the meaning of the original Greek word.
Here is John 3:16 from the Amplified Bible: "For God so greatly loved and dearly prized the world that He [even] gave up His only begotten (unique) Son, so that whoever believes in (trusts in, clings to, relies on) Him shall not perish (come to destruction, be lost) but have eternal (everlasting) life."
So to believe in Jesus means to: "trust in, cling to and rely on" Him!
I really like this three dimensional view of believe because it creates a picture of my relationship, as it is intended to be, with Jesus...not just as a first step to salvation but as an ongoing need on a daily basis to depend on Jesus. I like to think of faith like putting my weight on each board of a bridge that is crossing a deep canyon. Jesus is like each board that I trust to support the weight of my life...the weight of uncertainty, of cares, of questions of the things that are beyond my knowing and doing. A good self-check is to ask myself frequently: "Am I putting my weight on Jesus or on myself (or others)?"
Believe...a simple word that has great depth and practicality for this life and the next!