The exact nature of WAHI is beyond the understanding of common people like us.
It says in 37:102 .... YA BUNAYYA, INNI ARAA FIL MANAAMI .... [Literally, "O My Son! I have seen in my dream (or I have had a vision) ...."
37:102 And when he was old enough to strive along with him, Abraham said, “O My dear son! I have had a vision that I must give you to a life of test and tribulation for a Noble cause (37:107). So look, what do you think?” He said, “O My father! Do what you are commanded. God willing, you will find me of the steadfast.”
[Zibh and Zabh = Sacrifice = Disregard comfort for a Noble cause. Just as Qatl = To subdue, kill, fight, humiliate, bring low]
37:103 As both of them had surrendered themselves (to God), he made Ishmael further submit in gratitude. [Contrary to popular tradition, Abraham never envisioned or intended to slaughter his son. God does not play games with His servants. Literal ‘forehead to ground’ = complete submission in gratitude]
37:104 We called unto him, “O Abraham!
37:105 You have already affirmed the vision. We – This is so - We must reward the doers of good.”
37:106 This was a trial, clear in itself. [Leaving the prestigious office of Chief Priesthood in Babylon and now the comfort of Syria for the wilderness of Makkah]
37:107 We exchanged his life for a Momentous Sacrifice. [Please notice here the absence of the Biblical and the traditional myth of a 'ram' sent from the heavens. Also, note that slaughtering of a sheep or goat, by no means, can be considered a Momentous Sacrifice. 14:37, 37:102]