The central conceit in the poem is that the speaker and his lover were in a kind of sleep before they found each other. Prior to their meeting, anything of beauty that the speaker had ever seen or had was but a dream compared to the woman who is now his lover. Though born a Roman Catholic, Donne later became the Anglican Dean of St. Paul's Cathedral; we can see an example of his religious faith by the reference he makes in the first stanza to an old Christian legend:

I wonder, by my troth, what thou and I Did, till we loved? Were we not weaned till then? But sucked on country pleasures, childishly? Or snorted we in the Seven Sleepers’ den? (Emphasis added).

In the Christian tradition, the Seven Sleepers were young men who fled persecution at the hands of the Roman Emperor Decius. They retired to a remote cave to pursue a simple life of prayer and piety. When Decius heard about this, he punished the young men's defiance by having the entrance to the cave completely sealed. At the time, the men inside were blissfully unaware of what was going on, as they were all fast asleep. Nearly 200 years later, the mouth of the cave was opened, and the Seven Sleepers miraculously woke up, thinking they had only been asleep for a single day.

Donne uses the legend of the Seven Sleepers to reinforce the poem's central conceit. The speaker and his lover have spent their whole lives as if in a deep slumber, but they have woken up at long last and realized that they belong to each other. This is not just an expression of their intense physical passion; it also represents a true spiritual awakening of the lovers' respective souls.

In this poem, Donne is trying to convey the idea that he and his love were essentially created when they started to love one another.  Before that, they were nothing, or at least they were not anything like the real people they are now.

In the first stanza, Donne is trying to show what he and his love were like before they loved.  He compares them to little children or to country bumpkins. Then he uses the line you cite.  In that line, he is saying that their previous lives were like being unconscious or asleep.  He says that they were like people who were "snorting" -- meaning snoring.

According to eNotes' summary and analysis of this poem, the line refers to a legend of persecuted Christians who were walled up in a cave by Romans in Syria and left to die.  Instead, they miraculously slept rather than dying.  The poet is saying that he and his love were like these people -- not dead, but not really alive and conscious either.