What is the significance of this passage in "Dracula" by Bram Stoker? What are some literary devices? Expand.

“Oh, Madam Mina,” he said, “how can I say what I owe to you? This paper is as sunshine. It opens the gate to me. I am daze, I am dazzle, with so much light, and yet clouds roll in behind the light every time. But that you do not, cannot, comprehend. Oh, but I am grateful to you, you so clever woman. Madam”—he said this very solemnly—“if ever Abraham Van Helsing can do anything for you or yours, I trust you will let me know. It will be pleasure and delight if I may serve you as a friend; as a friend, but all I have ever learned, all I can ever do, shall be for you and those you love. There are darknesses in life, and there are lights; you are one of the lights. You will have happy life and good life, and your husband will be blessed in you.”