Does anyone ever pause to consider the sheer weight of what Castiel is doing here? Those blades are literally the only things capable of killing angels and Castiel gives the Winchesters two. He’s giving two humans a blade each that can kill his brethren, can kill him. What he’s basically doing is saying, “not only do I trust you enough not to use these on me, I trust you enough to allow you keep something so sacred and powerful that it can kill a soldier of Heaven.”
Do you think this ever happened before? Do you think an angel ever trusted anything with something so valuable like Cas is trusting two humans?
Remember, just one episode later Gabriel will scoff at the thought of giving the real thing to another being. You think I’d give Kali my real sword? That thing can kill me! The amount of trust required is staggering.
And yet here we see Castiel give two to a couple of humans. Beings that much of Heaven and the other angels have seen as insignificant for most of their time on the show.
Just something to think about.
According to the Book of Enoch all weapons were originally a secret of heaven. A group of angels chose to marry human women and shared these secrets with their families, that’s how humans first learned about any type of weaponry. Those angels were either cast into hell or locked up in heaven’s jail. To answer your questions, there is scripture of this happening before and things didn’t end well for those angels. Cas chose to give the Winchesters angel blades and holy fire, both of which were weapons of heaven, and he would have known he was risking his freedom by doing so.