What is this?

[Kenton H. Shepard, CMI]

I've seen a number of truss roofs built on the ground then craned into place. Nylon straps usually go around a strongback which has been tacked just under the truss peaks so that the weight/stress is distributed over more of the roof as it's lifted. The longer the strongback the better. I'd can't imagine succesfully raising a roof with that attachment alone.
It could be a lanyard attachment for roofers. It would work for that.

Since it was near an access hole and there was a furnace and water heater up there it was for lifting them up there, I'm thinking. In these days of big-time insurance claims employers don't want to risk paying for employee injuries. Cheaper to supply them with lifting equipment.

[Marcel R. Cyr]

It would be safe to assume at this point the the final deduction, and analyisis can finally be made by the one that took the picture in the first place.
The Panoramic view of circumstances of the beholder and all the speculated opinions of us combined, I am sure he can come to a conclusive conclusion.

Marcel