We know it when we get to The Promised Land. I cannot elaborate on how we know it, but we do - without a shadow of a doubt.
The Promised Land is the Land whereon God's Law is the Law of the Land. It is not a stationary spot. It moves with us because it our contact with the material reality that makes wherever we step Holy Ground. This happens when God's Law becomes the Law we want to live in accordance with. We are not subjected to God's Law. It is the Law of our free will. It is the Law we would live according to even if it was not God's Law. It is Our Law.
That Land is an island whereon only other Citizens can tread. No man-made laws can touch us there. No invader can reach us there.
The Holy Land is wherever the Holy touch. This is the Truth of the Promised Land, the real Land of Yisra'El.