“And Joseph said to his brothers, “I am dying. But God will surely visit you and bring you up out of this land to the land which he swore to Abraham, to Isaac and to Jacob.” '
Some of his brothers are clearly yet alive and he calls them and tells them that he is dying. And once he is dead God will then surely visit them and take them back to the promised land. Joseph is strongly aware that the covenant still stands firm and God's promises to their fathers must be fulfilled.
It would seem that he feels that, now that his position of authority will cease, their purpose in Egypt is done. They must by now have been a fairly large group numbering probably tens of thousands. But they have comfortably settled down and do not return to the land God has promised them, and eventually they will suffer for it. It is not wise to delay in obedience when God commands. And yet as the future reveals, when man fails God finds another way.