For those living in the Northern Hemisphere, nature provides a perfect backdrop for Advent.

We’ve gone from having 15 or so hours of daylight on June 21 to nine hours on Dec. 21.

Some people struggle with the shortening day. The increasing darkness leaves some people sad and even depressed.

The liturgical season preceding Christmas reminds us of the eons in history when the world did not know Christ, when sin and death held sway over the human condition because of Adam’s sin of pride.

Humanity was, as the prophet Isaiah said, “a people who walked in darkness.”

With the birth of Christ, however, that people “have seen a great light,” the prophet proclaimed. Christ is the Light of the world described in the prologue of St. John’s Gospel.

Why, then, does it feel, at times, that a darkness is encroaching on the world so much more in Advent 2011? A quick look at the headlines over the past year might lead one to conclude that things are hopeless: Christians persecuted throughout the Middle East; increasing restrictions on people of faith and conscience, even in our own country; a steady stream of reports of people who should be pillars of morality falling from grace (priests gone astray, respected football coaches allegedly found to have a seedy private life, etc.).

Did the first Advent of Christ have no effect at all?

Christ’s birth, which was the precursor of his becoming the sacrifice for our salvation, did not make it so we never again would have to contend with evil. At times, it seems like evil is gaining the upper hand. All the more reason for us to live more deeply the sacramental — and sacrificial — life to which we are called. Advent is a good time to renew that commitment.

The Christmas trees and holiday lights that start going up outside homes, in stores and on street corners right after Thanksgiving — even the orange Halloween lights we’ve begun to see in October — are more than mere decorations or ways to get people into a buying mood. They’re a response to a human need for light, especially when darkness surrounds them.

We Christians, however, needn’t turn our lights out on Dec. 26. We speak not only of our electric bulbs, but also the light that should shine from within ourselves.

It does seem, at times, as if the darkness is inescapable.

But Christ is the eternal Light of the world — and “the darkness has never been able to overcome it.”