The present tense in imperatives is usually to command the action as an ongoing process. (I learned this from Carl in another post. Thanks Carl!)
It is also passive which indicates that there is comfort that is being given from an outside source.
Could it be Englished as "continue letting yourselves be comforted?"
What I'm truly interested in is whether or not it is implied that there is an inability/resistance to continue recieving comfort?
On a personal note, I find that to be the case in my circumstances and wonder why the peace of God doesn't continually reign in my heart - is there something wrong with me? Why does God hate me so much?...I've never done anything FOR Him!

Sorry if this got too personal...just wondering if the use of the present passive imperative implies the constant need to be open to comfort and that we need to be aware of a tendency to resist being comforted.
Scotty