Many religions are about man's effort to reach God. Christianity is the opposite of religion it is a relationship with God. In Christianity, God came to us in the virgin birth of Jesus, because of His love for us, .
In the beginning of the Bible we are told how God created the world and how He created mankind in His own image. This is the ability of mankind to think, reason, understand, and have emotions. The world is created by God. It is impossible for something to come from nothing and it is even more impossible for life to come from non-life. The Bible tells us that mankind was created for fellowship with God to have a relationship with God in the Image that God created us.
As we all know Adam and Eve disobeyed God and sinned. Sin separated now sinful mankind from the Holy God. The earth is a fallen place where sin is being lived out in disobedience, sickness and death, all at the displeasure of God. Heaven is where God's will is being obeyed and Heaven is out of the presence of disobedience, sickness, sin and death.
This is where Jesus comes in, Jesus being God He created us, yet man's sin has separated us from God. In time, God took on the form of a man (became a physical man) in His body Jesus gave Himself and died on the cross. Dying physically so we can now have a Spiritual relationship with God. Three days later Jesus rose from death and showed Himself to be alive. Jesus is now alive and in a Spiritual body. The Bible tells us our physical eyes cannot see the Spirit or Heavenly realm, just as we cannot see radio waves yet know they exist.
Jesus said "My kingdom is not of this world" John 18:36 Jesus is referring to His kingdom where man is reunited with God in Spirit.
A Christian is a person who acknowledges their own human sinful nature and accepts the love of God to die on a cross for us. Being God, He then rose from death and currently is reuniting us into a living Spiritual Life with Himself.