How did these people see God's face? (Catholic perspective) In John 1:18, it seems no one has seen God's face:


  No one has ever seen God, but the one and only Son, who is himself God and is in closest relationship with the Father, has made him known.


And in Exodus 33:20, it is also mentioned that you cannot see God's face as you will die if you see his face.


  "But," he said, "you cannot see my face, for no one may see me and live."


Now we know that it is impossible to see God's face as you won't live after it, but somehow Moses saw his face and lived. Exodus 33:11:


  The Lord would speak to Moses face to face, as one speaks to a friend. Then Moses would return to the camp, but his young aide Joshua son of Nun did not leave the tent.


So did Aaron, Nadab, Abihu and the seventy elders of Israel. Exodus 24:9-11:


  Moses and Aaron, Nadab and Abihu, and the seventy elders of Israel went up 10 and saw the God of Israel. Under his feet was something like a pavement made of lapis lazuli, as bright blue as the sky. 11 But God did not raise his hand against these leaders of the Israelites; they saw God, and they ate and drank.


Oh, and Abram too. Genesis 12:7:


  Then the Lord appeared to Abram and said, “To your descendants I will give this land.” And there he built an altar to the Lord, who had appeared to him.


According to the Catholic Church, how did these people see God's face and live even though he clearly says no one can see his face and live?
Usually, in the old testament, when people are said to have seen God, this is referring to an angel sent by God. The case for Abraham is a good example. When Abraham saw God, he was looking at an angel sent from God, because God had not taken human form before Jesus. You can also see this when this angel goes to destroy the sodomites and his identity is made fairly clear. Manoa is also a good example of this. When the angle revealed himself to him and his wife, he says ... 


  We are doomed to die!" he said to his wife. "We have seen God


More in the context


  21Now the angel of the LORD did not appear to Manoah or his wife again. Then Manoah knew that he was the angel of the LORD. 22So Manoah said to his wife, "We will surely die, for we have seen God." 23But his wife said to him, "If the LORD had desired to kill us, He would not have accepted a burnt offering and a grain offering from our hands, nor would He have shown us all these things, nor would He have let us hear things like this at this time."…


People die when they see God because they are unclean and defilement cannot stand in the holiness and the glory of the lord. This is why there are exceptions. Isiah chapter 6 is good example:


  In the year that King Uzziah died, I saw the Lord, high and exalted, seated on a throne; and the train of his robe filled the temple. 2 Above him were seraphim, each with six wings: With two wings they covered their faces, with two they covered their feet, and with two they were flying. 3 And they were calling to one another: “Holy, holy, holy is the Lord Almighty; the whole earth is full of his glory. 4 At the sound of their voices the doorposts and thresholds shook and the temple was filled with smoke. 5 “Woe to me!” I cried. “I am ruined! For I am a man of unclean lips, and I live among a people of unclean lips, and my eyes have seen the King, the Lord Almighty.” 6 Then one of the seraphim flew to me with a live coal in his hand, which he had taken with tongs from the altar. 7 With it, he touched my mouth and said, “See, this has touched your lips; your guilt is taken away and your sin atoned for.”


When people are holy, they can stand in God's presence.