The type of figurative language used in this sentence is personification. There is a description of an object, which is the snow, “the soft, unbroken snow”, that helps explain an idea which is, that the snow was solid, that there was not need to feel afraid of walking over it. Let us take solidity as “solid base”, as something that you can rely upon. In addition, the word “soft” and “unbroken” together combined, form a powerful connotation. That the one who walks over it, can feel happy because it is soft and trustworthy because it is unbroken. “soft” could mean in this context, tranquility, pleasing to the senses.
