An extract from 'The Dialogue of the Seraphic Virgin by St. Catherine of Siena'
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How God induces the soul to look at the greatness of this Bridge, inasmuch as it reaches from earth to Heaven.
"Open, my daughter, the eye of your intellect, and you will see the accepted and the ignorant, the imperfect, and also the perfect who follow Me in truth, so that you may grieve over the damnation of the ignorant, and rejoice over the perfection of My beloved servants.
"You will see further how those bear themselves who walk in the light, and those who walk in the darkness. I also wish you to look at the Bridge of My only-begotten Son, and see the greatness thereof, for it reaches from Heaven to earth, that is, that the earth of your humanity is joined to the greatness of the Deity thereby. I say then that this Bridge reaches from Heaven to earth, and constitutes the union which I have made with man.
"This was necessary, in order to reform the road which was broken, as I said to you, in order that man should pass through the bitterness of the world, and arrive at life; but the Bridge could not be made of earth sufficiently large to span the flood and give you Eternal Life, because the earth of human nature was not sufficient to satisfy for guilt, to remove the stain of Adam's sin. Which stain corrupted the whole human race and gave out a stench, as I have said to you above. It was, therefore, necessary to join human nature with the height of My nature, the Eternal Deity, so that it might be sufficient to satisfy for the whole human race, so that human nature should sustain the punishment, and that the Divine nature, united with the human, should make acceptable the sacrifice of My only Son, offered to Me to take death from you and to give you life.
"So the height of the Divinity, humbled to the earth, and joined with your humanity, made the Bridge and reformed the road. Why was this done? In order that man might come to his true happiness with the angels. And observe, that it is not enough, in order that you should have life, that My Son should have made you this Bridge, unless you walk thereon."