Musar על מגילה 57:19

When he responded, Isaiah only volunteered for the שליחות, G–d's mission, not for the הליכה, which could have passed for his own initiative. G–d had to tell him then that at that point in time He needed a messenger only for the unpleasant part of the mission. This is why He said to him לך ואמרת, "go and say." Similarly, in our case, G–d wanted to provoke Pharaoh so that out of the additional "darkness" the contrast with the "light" of the redemption would be so much greater. In other words, יהי שם השם מברך, first afflictions, then peace, serenity. G–d Himself is with us even while we suffer, i.e. His own name will become greater only in the future. This is the meaning of עמו אנכי בצרה, "I am with Israel when it is in trouble" (Psalms 91,15). There is no greater trouble than that G–d's Presence must exile itself on account of our sins. In Exodus 1,14, וימררו את חייהם בעבודה קשה, "They made their lives miserable with hard labour," the word חייהם refers to that which gives us our strength, i.e. G–d. In other words, the Egyptians made our lives in the Celestial Regions bitter.

This may also explain why Joseph's burial in the Holy Land conferred spiritual elevation upon him. We have already explained that the reason G–d sent Joseph to Egypt ahead of the rest of Jacob's clan was to ensure that when Jacob and his family would begin their exile, they would come to a land where G–d's שכינה had already established a foothold. As a result, Joseph's body too would not taint the Holy Land when it would be buried in there.