Therefore, behold! I will again do marvelous things with this people, marvelous and astonishing things; and the wisdom of their wise men will perish, and the understanding of their discerning men will vanish or be hidden. (Isaiah 29:14 AMP)
It would at first glance at this Scripture appear that the Israelites had been serving God with their whole hearts and He was rewarding them. But the verse directly before this says they were honoring with their words but their hearts were far away. God wasn't happy with divided souls.
Instead of coming up with a punishment for Israel to force their hearts to love Him (Love isn't love when pressured.) He came up with a plan to show them, the common ones, miracles. Miracles, signs and wonders are to show God's love for them. They're not for fanfare. God was wooing Israel back to Him. He was doing signs and wonders to bring their attention to Him.
The mouths of the "wise men" He would hush. They were teaching false information.
God was giving the Israelites time to be away from lies and surrounded by His love in the wonders he would show them. He was giving them time for their hearts to warm and their words to flow from a love for Him.