You may recall that in much of Mahayana belief that we saw (in China), the everyday world, samsara, is understood to actually be the same thing as nirvana. That is a common part of Mahayana doctrine.
When we realize that the world we see around us is in fact also the world of nirvana, then we have in effect attained the consciousness of nirvana while still residing in this world. When we see that samsara is nirvana, then there is nowhere that we need to go to realize nirvana; we are already there.
So we see these two sides of reality in the form of the vajra, even as ultimate emptiness is also acknowledged.