Regarding Genesis 18:24-32. Help me understand how/why Abraham’s multiple supplications caused God to change His mind so many times in light of “I am the Lord and I change not”. Malachi 3:6
The context of the Malachi passage is the coming judgement and refinement of God's people as if by fire. It is God's unchanging mercy whereby the children of Jacob are not consumed in the process.
“Then I will draw near to you for judgment. I will be a swift witness against the sorcerers, against the adulterers, against those who swear falsely, against those who oppress the hired worker in his wages, the widow and the fatherless, against those who thrust aside the sojourner, and do not fear me, says the LORD of hosts. “For I the LORD do not change; therefore you, O children of Jacob, are not consumed. From the days of your fathers you have turned aside from my statutes and have not kept them. Return to me, and I will return to you, says the LORD of hosts. - Malachi 3:5-7*
In the passage from Genesis it is this very same mercy of God towards His people to which Abraham appeals in his repeated supplications.
Then Abraham drew near and said, “Will you indeed sweep away the righteous with the wicked? - Genesis 18:23
It is difficult, when reading through the account of Lot's life and choices, to see him as righteous but we have to remember that God looks on the heart. 2 Peter indicates that Lot's righteous heart was vexed by the wickedness of the city in which he had (foolishly, I add) chosen to live. Remember that we are shown in Gen. 15 (and Romans 4) how that righteousness is imparted through faith.
And he believed the LORD, and he counted it to him as righteousness. - Genesis 15:6
And so Abraham (very likely with his nephew Lot in mind) is basically asking God, "Don't you have any people in that city?", with full faith that, if there are any righteous (believers) God will act upon His unchanging mercy. It is interesting that Abraham does not ask God to save Lot by name, perhaps realizing that a wicked Lot would not come under God's mercy and so he appeals to mercy for the righteous in hope that Lot fits in that category. That Abraham importunately works God down from 50 to 10 demonstrates the depth of his faith in God's mercy. That God goes beyond the 10 and saves 4 demonstrates the depth at which His mercy and grace work together for the faithful righteous.