What is this temple?
Though not specifically confirmed, this temple is likely the remains of a Temple of the Triune. This conjecture is based largely upon the repeated references to the Triune's sacred number '3' throughout the cinematic. "By three they come. By three thy way opens..."
For most outwardly appearances, the Temple of the Triune was a benevolent religious body that preached selfless worship and devotion, peace, and focus on the individual for the people of Sanctuary. The number 3 was sacred to the Triune because it represented their three deities or kind guiding spirits: Dialon, Spirit of Determination, represented by a ram; Bala, Spririt of Creation, represented by a leaf; and Mefis, Spirit of Love, represented by a red circle.
Unbeknownst to outsiders, the Temple of the Triune was actually a cult created by the Prime Evils of Hell to convert humanity to the side of the Burning Hells. As members of the Cult of the Three became initiated, their hearts would darken as they learned the teachings of the true spirits they served: Diablo, Lord of Terror; Baal, Lord of Destruction; and Mephisto, Lord of Hatred.
Though the Temple of the Triune has dwindled on Sanctuary, relics of this religion still exist including this temple. At one point, the Temple of the Triune was led by Lilith herself and may be the reason this gateway even exists. For those familiar with
Diablo III, the Coven is considered a splinter group of the Triune.
Who is the mysterious pale figure?
Speculation has run rampant as to who the pale figure is that helped summon Lilith back to Sanctuary. Blizzard has yet to directly confirm the identity of this mysterious figure, but the community has largely conjectured that he is Rathma, based mostly on his appearance and him calling Lilith 'Mother' near the end of the cinematic. Because Lilith is considered the Mother of Sanctuary and many Necromancers (or priests of Rathma) have a similar appearance, this information was hardly conclusive.
Thanks to the original information provider
TeKo, the identity of the mysterious pale figure is almost certainly
Rathma. You can take the
Diablo IV press cinematic and import it into any video editing software that allows you to see markers. Markers leftover by Blizzard during a scene where you see the reflection of the cleric in the pale figure's eyes indicate that the pale figure is indeed described as Rathma as shown below.
Cinematic in Video Editing
Zoomed in view of markers during eye reflection scene
