Complex sentence: With each Ainu comprehending at first only those secondary ideas and themes most closely related to that primary idea-theme-thought of Ilúvatar's which pre-figured itself for that particular Ainu, these creative musical elaborations only gradually, through exposure to each other, become collaborative.
Split into simpler sentences: With each Ainu comprehending at first only those secondary ideas and themes most closely related to that primary idea-theme-thought of Ilúvatar's which pre-figured itself for that particular Ainu. These creative musical elaborations only gradually, through exposure to each other, become collaborative.