As salaamu alaikum,
There is no metaphor I know that can exactly describe memorizing Qur'an. It's more crunchy and sweet than a box of chocolates, and more time and energy consuming than a marathon. It is a way of life. It is a thing that fills the whole soul, thoughts, and aspirations of a person before one knows it. It is a correcting lens that gives perspective to the physical and spiritual eye. It is a soothing balm that covers and heals the bruises and suffering of the heart. It is the friend who always knows just what to say even when one doesn't want to hear it. It is conversation with Allah Almighty. Read it. Know it. Well.