A cross post from SHC with spoilers!
First off the descent of God is not a literal myth. Its based on several mythologies, mostly Aztec in Silent Hill's case. (looking at the rituals to God and the references in the Lost Memos about human sacrifice to the sun, I am pretty sure its from Aztec rituals.)
In the beginning, people had nothing. Their bodies ached, and their hearts held nothing but hatred. They fought endlessly, but death never came. They despaired, stuck in the eternal quagmire.
Myth - "2. Birth" 2. Birth
A man offered a serpent to the sun and prayed for salvation. A woman offered a reed to the sun and asked for joy. Feeling pity for the sadness that had overrun the earth, God was born from those two people.
This means that God was already in existence as the sun, it corresponds with numerous evidence about God being a solar deity. Did they literally descend the sun? No. An embodiment maybe. Fact is God is the sun and the sun is God.
God made time and divided it into day and night. God outlined the road to salvation and gave people joy. And God took endless time away from the people.
This would mean the sun started to rise and set. In Aztec thought they did sacrifices to continue the movement of the sun. With out movement, with out time, people are lost.
God created beings to lead people in obedience to Her. The red god, Xuchilbara; the yellow god, Lobsel Vith; many gods and angels. Finally, God set out to create Paradise, where people would be happy just by being there.
Notice that the two gods are colors of the sun. Although in SH2 Xuchilbara/paba is also associated with the night and water/mist. In the Crimson Tome its also said that Xuchilpaba's blessings are a wither flower and the last struggles of a dying man. (Underworld deity?)
But there God's strength ran out, and She collapsed. All the world's people grieved this unfortunate event, yet God breathed Her last. She returned to the dust, promising to come again.
Push the pause button right here. Pay attention to all of this. God lost strength and "died" and everyone grieved. This is not literal. This is talking about the movement of the sun. In many cultures, Egyptian, Babylonian, and Greek to name a few believed the sun's movement when it was setting to it "dying" and returning to the underworld. This is also in Aztec mythology which has no connections to the other three cultures named. It developed independently.
Ishtar is mentioned in a memo in 2, she is the ONLY god named who is NOT a fictional deity. (I think the Christian God too is mentioned, but not in an important context like this.) Anyone aware of Sumerian and Babylonian mythology is aware of Ishtar's most famous myth in which after the bull of heaven was slain by Gilgamesh Ishtar performs funeral rites to his widow, her sister, the underworld goddess Ereshkigal. She likewise does this to seize power of the underworld. When she descends she "dies", (She also literally dies in the underworld later.) this is also true for gods in Aztec myth, such as Itzpapalotl, which is the dead form of Cihuacoatl. Ishtar is Resurrected which has to do with the reference in two with Xuchilpaba because it's about rebirth and Resurrection of the dead + Acacia.
After Ishtar is brought back to life Ereshkigal demands a replacement. Dumuzi or Tammuz, her husband is chosen to go into the underworld for 6 months of the year and his sister Gestianna for the other 6 months. In the bible, Ezekiel 8:14, a woman is weeping for Tammuz because he descended to the underworld and "died". Ishtar nor Tammuz nor his sister Gestianna are actual solar deities though. After awhile Ereshkigal remarries a god named Nergal ( A god the other gods gave to her to appease her.) who is also the sun god Utu. Every time the sun sets as Utu he is reunited with his wife, Ereshkigal, in the underworld. (FYI Ereshkigal cannot leave the underworld.) When he is with her, they call him Nergal.
So in this myth I am pretty sure its talking about God "dying" by going to the underworld each night and like the bible with Christianity irl, has been grossly misinterpretated as literal. I also think Xuchilpaba, in the Native religion, has something to do with "God's rebirth". But it was possible this is taken out of the Order since its so different. Now knowing this I can make a synopsis that perhaps the human sacrifice in Native religion was to keep the "ollin" (Nahuatl) or movement going.
If you have some time I suggest reading this Aztec myth, you'll see parallels to the Order's myths. I've also made a video on it to clear up confusion.