In short, the meaning of “He doeth whatsoever He willeth” is that if the Manifestation says something, or gives a command, or performs an action, and believers do not understand its wisdom, they still ought not to oppose it by a single thought, seeking to know why He spoke so, or why He did such a thing. The other souls who are under the shadow of the supreme Manifestations are submissive to the commandments of the Law of God, and are not to deviate as much as a hairsbreadth from it; they must conform their acts and words to the Law of God. If they do deviate from it, they will be held responsible and reproved in the presence of God. It is certain that they have no share in the permission “He doeth whatsoever He willeth,” for this condition is peculiar to the supreme Manifestations.
Praise be to God, the Eternal that perisheth not, the Everlasting that declineth not, the Self-Subsisting that altereth not. He it is Who is transcendent in His sovereignty, Who is manifest through His signs, and is hidden through His mysteries. He it is at Whose bidding the standard of the Most Exalted Word hath been lifted up in the world of creation, and the banner of “He doeth whatsoever He willeth” raised amidst all peoples. He it is Who hath revealed His Cause for the guidance of His creatures, and sent down His verses to demonstrate His Proof and His Testimony, and embellished the preface of the Book of Man with the ornament of utterance through His saying: “The God of Mercy hath taught the Qur’an, hath created man, and taught him articulate speech.” No God is there but Him, the One, the Peerless, the Powerful, the Mighty, the Beneficent.
— Baha’u’llah, Epistle to the Son of the Wolf. Trans. Shoghi Effendi 1988: 1