Quote from the lecture:

Having introduced the first few churches, we have now arrived at the heart. The church Thyatira is related with the heart, which is related with the chakra Anahata (Sanskrit). Thyatira is the 4th of the 7 churches; being the 4th, we understand that it will have a relationship with the number 4, but also when we look at the structure of the Tree of Life and count from the bottom sphere up, we arrive at the 4th: We are talking about Netzach, which is related with the mind, with the mental body. When we study this church Thyatira we are really dealing with important qualities of the heart and mind.