Ammon and Moab were the sons of Lot, and Lot was the son of elder brother of Abraham (Abram) by name Haran. (Gen. 11: 31) They lived in the Dispensation of Concience. They were judged by God as righteous or wicked, how they obeyed their concience. In (II Peter 2: 7,8) we read about righteous Lot whom God delivered from the destruction of Sodom and Gomorraw. In the New Testament the Holy Spirit through St. Peter declared, Lot was righteous, according to his concience.
But some New Testament preachers weigh Lot in the balance of New Testament law, instead of weighing in the balance of Concience! The result is they preach that Lot was sinner or he was a cause for an abominable birth of two nations. Now let us consider their cases, how God viewed them? We know Adam’s children married among themselves as none were available out side. God did not count it sin or inappropriate. During the Despensation of Concience only their concience was the Law of God. Obeying their concience is accounted righteousness. Accordingly the marriage of Adam’s children was act of righteousness. Till the law of Moses was established, or a written law was established, the acts of concience period were righteous if their concience accepts their actions. Abraham and Lot belong to Concience Period. Though their actions were against the Law of Moses, but agreed by their concience, and they were righteous, in the sight of God.
Abraham said that Sarah was his sister, and she was not the daughter of his mother but daughter of his father. (Gen. 20: 10-12) God agreed their marriage and gave Isaac to them, and in that geneology Jesus was born. But as per Mosaic Law Adam would be a sinner by marrying his sister. (Lev. 18:9) But Mosaic Law is not applicable on Abraham. Similarly Lot was a cause unknowingly, for the birth of Ammon and Moab through his two daughters. As per Mosaic Law the daughters of Lot were sinners, (Lev.18:7) but they were not under Mosaic Law, God accepted them and never blamed their actions with their father. Then one may ask a question that why God forbidden their entry into the congregation of Israel? As God prohibits their entry into the congregation of Israel for ever, we understand that they had done some serious offence. What was it? In (Duet. 23: 3-6) and ( Neh.13: 1,2) we read that when the people of Israel journeyed from Egypt to Canaan under Moses, through wilderness, and due to tiresome journey, they need water, and comfort. Israelites were the children of Abraham and Ammonites and Moabites were the children of Lot, who was the son of Haran, the elder brother of Abraham. God also warned Israelites that He will not give any land of Ammonites and Moabites as God had given that land to Lot. The children of Lot, the Ammonites and Moabites should have welcomed them with bread and water, but instead, they (King of Moab, called Balak) hired Balaam the prophet of Pethor of Mesopotamia to curse them. Also due their subtil plan adviced by Balaam, their life of separation was defiled and the wrath of God came on Israelites and 24000 people died.(Num.25: 1-9) So God gave such a verdict that Ammonites and Moabites shall not enter the congregation of Israel for ever. (Duet. 23: 3-6)