There is nothing we can do to earn our way into heaven or to prove our worth. As for "just believing" in God, even demons do that and don't get a "get into heaven free" card. The belief and faith is about Jesus Christ... who He is and what He has done.
John 3:16 "16 “For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life."
John 14:6 "Jesus said to him, “I am the way, and the truth, and the life; no one comes to the Father but through Me."