The stone laid in Zion is your own human imagination, the very thing the ordinary man rejects and overlooks, set down as the one foundation on which everything he builds must rest. Zion is the eternal home of God, meaning within you, and the stone laid there is precious and tested because assuming a state and staying with it has never once failed to bring that state to pass. This is God's cornerstone, and it is the power you carry and mostly ignore.
He that believeth shall not make haste, and the calm is the point. A man who knows his imagining is the foundation feels no need to rush or force the outcome. He has made his assumption, he trusts it as sure, and he leaves it to harden into fact in its own time. Impatience betrays a man who does not yet believe his own inner act. Certainty rests, and waits without strain, because it knows the stone already holds.