YHWH said to Cain, “Why are you angry, and why has your face fallen? If you do well, will you not be accepted? And if you do not do well, sin is crouching at the door. Its desire is for you, but you must rule over it.”

This is what God said to someone who was offering sacrifices to him which he would not accept. That is from Genesis 4. Fastforward to Revelation 4:

After this I looked, and behold, a door standing open in heaven! And the first voice, which I had heard speaking to me like a trumpet, said, “Come up here, and I will show you what must take place after this.” At once I was in the Spirit, and behold, a throne stood in heaven, with one seated on the throne.

The voice, as is established in chapter 1, is the voice of a glorified Jesus. John has already been in the Spirit, worshiping, and already begun to see visions. But here there is some sort of transition: he passes through a doorway to go before the throne. What happens to lead to this passage?

Between the initiation of the visions in chapter one and the doorway into the heavens in chapter four what we find are a series of exhortations for the seven churches which almost all include admonitions to repent of sin.

When you think about it, the doorway to the Tabernacle or Temple was similar.  The altar was placed in the fore-court, as was the laver for cleansing.  You went into the sanctuary (if you had access) by way of cleansing and sacrifice.  You dealt with sin to get in the door.  Inside the sanctuary was bread and beer (strong drink was there and wine wasn’t allowed, so that leaves beer), and the end result of the cycle of sacrifices was food from the altar.  So inside the door you get to eat and drink, but only after you’ve dealt with sin crouching at the door.

The Exodus follows the pattern as well.  God brings Israel across the Red Sea and destroys Egypt, promising that none of their plagues will touch them, and then God feds them mannah and water from the rock.

So if the story of Cain and Abel fits with this, the door where sin was crouching for Cain was their place of worship.  In some way he was refusing to leave them behind.

This, is one indication, by the way, that when we gather for public worship on the Lord’s day, we should, toward the beginning, confess our sins and receives God’s forgiveness.