I'm a young earth Christian (Bible literalist) and believe that the first pure religion was Adam's relationship with God, the Creator. There were no barriers or traditions to separate Adam from God. The Bible states that the Creator is Christ (Colossians 1:16). The Bible also states that Christ is the Word and that "in the beginning was the Word and the Word was with God and the Word WAS God" (John 1:1). Therefore, Christ was from the beginning which means that Adam believed in Christ.
Also, the God that the Israelites followed was also Christ:
1 Corinthians 10:1-4, "Moreover, brethren, I would not that ye should be ignorant, how that all our fathers were under the cloud, and all passed through the sea; And were all baptized unto Moses in the cloud and in the sea; And did all eat the same spiritual meat; And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ."
No other religion on earth preceded God's first contact with man which occurred in the Garden of Eden.
And before Eve was created there was no sin separating Adam from God either! Adam, a biblical archetype who represents all mankind in Genesis, was the only man to know what it's like to be without sin, in a state of physical perfection, and one with God in paradise.
Which brings up an interesting situation.
As you know Adam as the agent of original sin represents all mankind.
And mankind did not fall and become separated from God by sin through Adam's eating the forbidden fruit until AFTER Eve was created.
So if we go back chronologically to a time BEFORE Eve was created we have a period of time where Adam was in a heavenly state of physical perfection, without sin, in paradise and in spiritual oneness with God.
But even though Adam was without sin and one with God, God himself said that Adam was so "alone" it was "not good."
Gen 2: 18 And the LORD God said, It is not good that the man should be alone; I will make him an help meet for him.
So how could Adam have been so "alone" it was "not good" BEFORE he was separated from God by sin??????
God saw Adam was lacking a mate and created Eve, but how could Adam have been lacking anything while he was without sin and one with God??????
Now as you know, we will not have a mate in heaven, only sinless oneness with God.
Matthew 22: 30 For in the resurrection they neither marry, nor are given in marriage, but are as the angels of God in heaven.
So who in their right mind would want to spend an eternity in heaven so "alone" it's "not good?"
Friends will keep you sane, Love could fill your heart, A lover can warm your bed, But lonely is the soul without a mate.
- David Pratt
Heaven will be no heaven to me if I do not meet my wife there.
Andrew Jackson
I don't believe in an afterlife, so I don't have to spend my whole life fearing hell, or fearing heaven even more. For whatever the tortures of hell, I think the boredom of heaven would be even worse.
- Isaac Asimov