Woe is a pronouncement of judgement from the Lord (Isaiah 5:8-10)
Woe is a warning of destruction from God (Isaiah 5:11-17)
Woe is a terrifying state to be in (Isaiah 5:18-25)

If Isaiah deserved the same judgement and destruction that Israel deserved, why did he receive mercy?
Answer: Because rather than not regarding the LORD (Isaiah 5:12b), rather than making a mockery of God (Isaiah 5:19), and rather than rejecting and dispising His word (Isaiah 5:24b), he was humbled and confessed His sin before Him (Isaiah 6:1-5)
if you will not humble yourself before the LORD and continue in your sin, the day is coming when you will be humbled when you are judged and cast into hell where there will forever be woe ahead of you (Revelation 8:7-13)