And Abraham answered and said, Behold now, I have taken upon me to speak unto the Lord, which am {n} but dust and ashes:

(n) By this we learn, that the nearer we approach to God, the more our miserable estate appears, and the more we are humbled.

Wesley's Notes

18:27 Behold now, I have taken upon me to speak unto the Lord, who am but dust and ashes - He speaks as one amazed at his own boldness, and the liberty God graciously allowed him, considering God's greatness, he is the Lord; and his own meanness, but dust and ashes. Whenever we draw near to God, it becomes us reverently to acknowledge the vast distance that there is between us and Him. He is the Lord of glory, we are worms of the earth.

Matthew Henry's Concise Commentary

18:23-33 Here is the first solemn prayer upon record in the Bible; and it is a prayer for the sparing of Sodom. Abraham prayed earnestly that Sodom might be spared, if but a few righteous persons should be found in it. Come and learn from Abraham what compassion we should feel for sinners, and how earnestly we should pray for them. We see here that the effectual, fervent prayer of a righteous man avails much. Abraham, indeed, failed in his request for the whole place, but Lot was miraculously delivered. Be encouraged then to expect, by earnest prayer, the blessing of God upon your families, your friends, your neighbourhood. To this end you must not only pray, but you must live like Abraham. He knew the Judge of all the earth would do right. He does not plead that the wicked may be spared for their own sake, or because it would be severe to destroy them, but for the sake of the righteous who might be found among them. And righteousness only can be made a plea before God. How then did Christ make intercession for transgressors? Not by blaming the Divine law, nor by alleging aught in extenuation or excuse of human guilt; but by pleading HIS OWN obedience unto death.