To live in this world, you must be able to do three things: to love what is mortal; to hold it against your bones knowing your own life depends on it; and, when the time comes to let it go, to let it go.

This quote is suggesting that in order to be able to survive in life, we must learn how to appreciate the things that are precious yet fleeting. This means that although we may experience pain when these things change or end, we must be able to love them while they are with us. We must treasure and value these moments, since our own lives often depend on them. But when the time comes for them to go, we should also accept it and let them go without clinging too strongly to them.