The second reason is expressed in the nineteenth verse; God had chosen Abraham that he might command his children and his household after him to keep the way of the Lord, to do justice and judgment that the Lord might fulfil His promise to Abraham. That is to say, as it was only by obedience and righteousness that Abraham and his seed were to continue in God's favour, it was fair that they should be encouraged to do so by seeing the fruits of unrighteousness. So that as the Dead Sea lay throughout their whole history on their borders reminding them of the wages of sin, they might never fail rightly to interpret its meaning, and in every great catastrophe read the lesson "except ye repent ye shall all likewise perish." They could never attribute to chance this predicted judgment. And in point of fact frequent and solemn reference was made to this standing monument of the fruit of sin.
As yet there was no moral law proclaimed by any external authority. Abraham had to discover what justice and goodness were from the dictates of his own conscience and from his observation upon men and things. But he was at all events persuaded that only so long as he and his sought honestly to live in what they considered to be righteousness would they enjoy God's favour. And they read in the destruction of Sodom a clear intimation that certain forms of wickedness were detestable to God.
The earnestness with which Abraham intercedes for the cities of the plain reveals a new side of his character. One could understand a strong desire on his part that Lot should be rescued, and no doubt the preservation of Lot formed one of his strongest motives to intercede, yet Lot is never named, and it is, I think, plain that he had more than the safety of Lot in view. He prayed that the city might be spared, not that the righteous might be delivered out of its ruin. Probably he had a lively interest in the people he had rescued from captivity, and felt a kind of protectorate over them as he sometimes looked down on them from the hills near his own tents. He pleads for them as he had fought for them, with generosity, boldness and perseverance; and it was his boldness and unselfishness in fighting for them that gave him boldness in praying for them.