Just because you say you are not an atheist does not mean that you know God.  To acknowledge His existence should mean that we want to know Him and align ourselves to Him.  Christians believe that He has been made known in the Person of Jesus of Nazareth as God’s promised Messiah.  If God exists, then it matters what kind of person I am.  I am accountable to Him.  I should love Him and align my life with what He has made known about Himself.

“But without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him.” Hebrews 11:6 (NKJV)