Sling out - A similar metaphor for violent ejection occurs in Isaiah 22:18 (see the note).
At this once - Or, “at this time.” Previous invasions had ended either in deliverance, or at most in temporary misfortune. God’s long-suffering is exhausted, and this time Judaea must cease to be an independent nation.
That they may find it so - Omit “so,” and explain either
(1) “I will distress them” with the rigors of a siege “that they may feel it, i. e., the distress; or,
(2) “that they may find” Me, God, that which alone is worth finding.