Komentarz do Rodzaju 37:5

ויגד לאחיו, this too was an ill advised move. Had he been more mature he would have kept the contents of such a dream to himself.

ויחלום יוסף חלום. Joseph had a dream. Why did Joseph add to his brothers' hatred of him by telling them of his grandiose dreams? Furthermore, knowing as he did that the brothers hated him fiercely, why did he accept his father's mission (verse 14) and venture "into the lion's den?" (According to Bereshit Rabbah 84,11 even Jacob could not understand Joseph's preparedness to accept his mission) Perhaps Joseph went to tell his brothers that they were wrong in ascribing his dreams to his ambitions, but that for some resaon G'd planned to elevate him to a high position and that Jacob's agreeing to send him on this mission was a sign that all of this had been approved by G'd. He may have hoped to assuage their hatred of him by accepting the misssion.

ויחלום....ויאמר, he dreamed, and wanted to make them feel bad seeing that they had displayed jealousy of his father’s love for him, and had allowed that jealousy to deteriorate into hatred of him. Seeing that eventually, Joseph’s rise to power was due to his handling of the harvest in Egypt, the details of the dream were: והנה קמה אלומתי, the symbol of my success, i.e. my sheaf of grain remained erect, whereas your sheaves bowed down to me. It was a fact that in due course the grain harvest was the cause of the brothers prostrating themselves before Joseph.