"The day had come...."- Which 'day' is suggested here? What is the significance of this 'day'?

This line is extracted from one of the most famous short stories of Katherine Mansfield, The Fly,  extracted from The Dove's Nest.

               The 'day' when Macey had handed the boss the telegram of his son's death.

 This line indicates how the news of his only son's death came as a staggering blow upon the boss. The boss, a prosperous, active businessman had all his hopes around his only son. But the death of his son had snatched  all his hopes from him. The entire expression signifies the profound sense of loss and sorrow of the old father at the death of his only son. But the significance of sorrow, communicated in it, is deep enough.