His power will be great, but it will not be his own. He will cause terrible destruction and succeed in whatever he does. He will destroy the mighty men along with the holy people.
KJV
And his power shall be mighty, but not by his own power: and he shall destroy wonderfully, and shall prosper, and practise, and shall destroy the mighty and the holy people.
ASV
And his power shall be mighty, but not by his own power; and he shall destroy wonderfully, and shall prosper and do his pleasure; and he shall destroy the mighty ones and the holy people.