What is the wisdom behind the variation in Allah's methods of addressing humanity, while preserving free will?

If God were to speak to all humanity and reveal to them, the wisdom behind obligation (taklif) and the test of humankind through belief in the unseen and affirming the messengers would be lost. God's wisdom necessitated choosing messengers from among humans to convey His commands and prohibitions. Allah says: "Allah chooses messengers from the angels and from the people. Indeed, Allah is Hearing and Seeing." And Allah knows best who deserves this selection, so He singles them out for revelation, as He said: "Allah knows best where to place His message." If revelation were given to all creation, that great wisdom and benefit would vanish, and the believer would not be distinguished from the disbeliever.