And the roof of thy mouth like the best wine for my beloved, that goeth down sweetly, causing the lips of those that are asleep to speak. The roof of thy mouth like the best wine - The voice or conversation of the spouse is most probably what is meant.
Causing the lips of those that are asleep to speak - As good wine has a tendency to cause the most backward to speak fluently when taken in moderation; so a sight of thee, and hearing the charms of thy conversation, is sufficient to excite the most taciturn to speak, and even to become eloquent in thy praises.