I will be glorified in … thee. The thought and the phrase come from Exodus 14:4; Le Exodus 10:3. Ezekiel reproduces it in Ezekiel 39:13. God is glorified, or, as in the next clause, sanctified, when his power and holiness are manifested in righteous judgment.
(For "sanctified," see Ezekiel 38:16 : Numbers 20:13.