"The Lord, the Lord Almighty, called you on that day to weep and to wail, to tear out your hair and put on sackcloth. But see, there is joy and revelry, slaughtering of cattle and killing of sheep, eating of meat and drinking of wine! 'Let us eat and drink,' you say, for tomorrow we die!'" NIV translation
After God delivered them from the hand of the Assyrians, they were called to repentance and to acknowledge Him. Instead, they continued acting in the same manner. They were going along as if nothing had happened. This is a reminder to us that, coming to faith in Jesus Christ, involves a change of mind to agree with God and turn to Him.
"The Lord Almighty has revealed this in my hearing: 'Till your dying day this sin will not be atoned for,' says the Lord, the Lord Almighty." NIV translation
Even after their deliverance, they had refused to acknowledge God.
Isaiah informs them that this sin will not be atoned for. So, how can this be? How can a sin not be atoned for through the blood of Jesus Christ?
In Matthew 12, Jesus said that blasphemy against the Spirit will not be forgiven. This was speaking of attributing the work of God to another (in that case it was Satan).
Judah had done the same thing in the fact that they had not acknowledged the redemptive work of God. The Holy Spirit had moved in the hearts of men to cause the Assyrian army to abandon their plans. Instead of acknowledging the hand of God, they had credited others with the fact that they had been saved from the Assyrians.
This demonstrated their lack of faith and we are reminded that without faith it is impossible to please God.
"This is what the Lord, the Lord Almighty, says: 'Go, say to this steward, to Shebna the palace administrator: "What are you doing here and who gave you permission to cut out a grave for yourself here, hewing your grave on the height and chiseling your resting place in the rock?"'" NIV translation
In this passage, we see that the "failure of faith" had started with the leadership in Jerusalem. The palace administrator was second only to the king and, instead of trusting in God, he was busy preparing himself a choice final resting place.