“Winter, which strips the leaves from around us, makes us see the distant regions they formerly concealed; so does old age rob us of our enjoyments, only to enlarge the prospect of eternity before us.”
Meaning: Imagine you are standing in the woods during winter. The trees are barren. There are no leaves to hinder your view. You can see much deeper into the woods than you can in the summer.
It is the same with youth and old age. When you are young, your day to day activities are the leaves. It is hard to see past what is coming tomorrow. When you are old, the leaves fall away. You are in the winter of your life. You start to look past day to day experiences and spend more time thinking about what lies beyond, and what comes next.