What is the wisdom behind procreation, striving in life, and working, if the ultimate end is the grave?

The grave is the first stage of the Hereafter, not the final destination. The life of this world was created for humanity to populate it with obedience to Allah, and death is a rest for the believer and a transition to something better. A person must realize that the purpose of their existence is to worship Allah, and caring for children and raising them in faith is part of this worship, and it is considered a treasure for the parents in the Hereafter.