The manga is skipping a LOT of content from the LN. When Roya summons his snake, Cynthia gets a vision of her goddess Petra along with a blessing. A serious injury that was impossible to heal is suddenly gone, which is going to greatly extend her life. This convinces Cynthia and then her people that Roya is their Holy Son who has the favor of their goddess. In their eyes, he is now their religious leader, and they are 100% loyal to him. Just how important this scene is isn’t conveyed at all.
The manga is skipping a LOT of content from the LN. When Roya summons his snake, Cynthia gets a vision of her goddess Petra along with a blessing. A serious injury that was impossible to heal is suddenly gone, which is going to greatly extend her life. This convinces Cynthia and then her people that Roya is their Holy Son who has the favor of their goddess. In their eyes, he is now their religious leader, and they are 100% loyal to him. Just how important this scene is isn’t conveyed at all.