What is the wisdom behind Abraham's saying to the king that Sarah was his sister, and Lot's offering his daughters to his people?

Scholars have differed regarding the reason why Ibrahim (peace be upon him) said about Sarah that she was his sister. It was said that the king's law prevented him from accosting married women, or he would kill him, or force him to divorce her, or that a brother has more right to marry his sister. It seems more likely that the king would kill the husband of any woman he desired, and Ibrahim's statement was not an outright lie but rather a dissimulation (tawriya), as Sarah was his sister in Islam. Even if it were an outright lie, it is not blameworthy in Islamic law because it was to save a respected soul, especially the soul of a prophet. As for Lot's statement to his people: "These are my daughters, they are purer for you," the intention was to guide them to his daughters after they entered his religion, or he guided them to the women of their own people to marry them instead of committing indecency.