And in that water she is re-formed, as new. The word mikvah comes from the same root as the word tikvah - Hope. The essence of hope is that we are not bounded and trapped by our present reality. Hope says that we can connect to that which is outside and beyond ourselves. To the Source.
Every mikvah is like a little sea.
50 represents the transcendent. The gateway to that which is beyond. This is the essence of purity. Life is not frozen in stone. Hope tells us that we can return to the world of water to be become purified.