Which church is the one true church?

     People mistakenly think that there is an earthly organization that is the one true church.  The true church is not an organization, not a series of buildings, but the body of true believers.  The true church consists of those who are regenerate; that is, it consists of those who are the true Christians.  There are, however, churches that are Christian and churches that are not Christian.
     But you might ask how we can tell if a church is Christian or not?  The answer is simple once we understand what makes someone a Christian or not.  I've reproduced part of the information found at www.carm.org/doctrine/grid.htm which lays out the essential and non essential doctrines.  Once we know what is essential, we can then look at a church and see if it is Christian or not.

1. Primary Essential Doctrines  
   Cannot be denied and still be Christian since the scriptures openly declare that to deny them is to bring judgment.
   1. Jesus is both God and man (John 1:1,14; 8:24; Col. 2:9; 1 John 4:1-4).
   2. Jesus rose from the dead physically (John 2:19-21; 1 Cor. 15:14).
   3. Salvation is by grace through faith (Rom. 5:1; Eph. 2:8-9; Gal. 3:1-2; 5:1-4).
   4. The gospel is the death, burial, and resurrection of Jesus (1 Cor. 15:1-4; Gal. 1:8-9).
   5. There is only one God (Exodus 20:3; Isaiah 43:10; 44:6,8)
2. Secondary Essential Doctrines 
   Not explicitly stated in Scripture as essential but they are derivatively necessary.
   1. God exists as a Trinity of persons:  Father, Son, and Holy Spirit. (See Trinity)
   2. Jesus was born of the Virgin Mary (nature of incarnation)
3. Non-Essential Doctrines -
   Can be believed or not and it does not affect whether or not one is Christian or not.
   1. Predestination, election, limited atonement, and free will
   2. Communion every week, monthly, or quarterly, etc.
   3. Saturday or Sunday Worship
   4. Pre, mid, post trib rapture.
   5. Premill, Amill, post millenialism, preterism.
   6. Continuation or cessation of the charismatic gifts
   7. Baptism for adults or infants

     Therefore, we can see that if a church or denomination would deny that Jesus is God in flesh, or physically risen from the dead, then it would not be Christian.  Furthermore, we could have two different churches that disagree on the non-essentials, but are still Christian since they affirm the essentials. 

Cults

     The reason the cults are not Christian is because they deny the essential doctrines of Christianity.  Mormonism, for example, denies that there is only one God in all existence and it denies that salvation is by grace through faith.  The Jehovah's Witness organization, denies the Trinity, the deity of Christ, salvation by grace, and Jesus' physical resurrection.  Therefore, they are not Christian, either. 
     So, if we know what the essentials are, we can then look at a church or denomination (or even a person) and ascertain if that church is Christian or not by whether or not it denies the essential doctrines that make Christianity Christian.
    Finally, to answer the question of which church is the true church, the true church is the cross section of believers in all churches that adhere to the essential doctrines of Christianity.