What is the explanation of the saying of Imam Ali, may God be pleased with him: "He is the one whose hereafter is happy and whose worldly life is miserable," and "How amazing it is for one who works for this world, yet is provided for in it without effort, but does not work for the Hereafter, yet is provided for in it only through effort"?

The two statements attributed to Imam Ali (may Allah be pleased with him) have not been confirmed as authentic. Assuming their authenticity:

The first statement, "He whose Hereafter is happy and whose worldly life is wretched," is understood in terms of what appears to people concerning an individual's state. Happiness and wretchedness in this world may be judged by human standards, whereas true happiness lies in attaining Paradise and escaping Hellfire. One cannot definitively know in this world who is wretched and who is happy; it is only a conjecture.

As for the second statement, "How astonishing is he who works for this world, though he is provided for in it without effort, yet does not work for the Hereafter, though he will not be provided for in it except through effort," its meaning is that it is astonishing how a person strives for sustenance that is already guaranteed for him in this world, while neglecting to work for the Hereafter, where he will only receive what he has presented. The wise person makes his worldly life a means to his Hereafter.