Alma 28:14

and thus we see the great call of diligence of men to labor in the vineyards of the Lord; and thus we see the great reason of sorrow, and also of rejoicing: sorrow because of death and destruction among men, and joy because of the light of Christ unto life.

And so we see why people need to work hard for the Lord. We see why there is great sadness and also great joy. Sadness because of death and destruction among people. Joy because of the light of Christ that leads to life.

And you can see how urgent it is for people to work hard in the Lord’s vineyard. You can see the reason for both sorrow and joy: sorrow over death and destruction, and joy over the light of Christ that leads to life.