NET
21 For the Lord will rise up, as he did at Mount Perazim; he will rouse himself, as he did in the Valley of Gibeon, to accomplish his work, his peculiar work, to perform his task, his strange task.
Darby
21 For Jehovah will rise up as on mount Perazim, he will be moved with anger as in the valley of Gibeon; that he may do his work, his strange work, and perform his act, his unwonted act.
KJV
21 For the LORD shall rise up as [in] mount Perazim, he shall be wroth as [in] the valley of Gibeon, that he may do his work, his strange work; and bring to pass his act, his strange act.