The parable at the beginning of chapter 5 was likely proclaimed at the Feast of Booths, when Israel celebrated God's blessings of the harvest. It begins in the style of a festival song, filled with harvest imagery, but soon turns into an idictment. Parables of this type are designed to get listeners to pass judgement on themselves (think of David's response to the prophet Nathan). The narrator elicits his listeners' outrage at a hypothetical injustice. Their response is then applied to a real situation involving the audience. Only then do they realize that the story is about them.
God condemns 6 sins: (1) exploiting others; (2) drunkenness; (3) taking pride in sins; (4) twisting moral standards; (5) conceit; (6) perverting justice. Because of these sins, He will discipline Israel using the Assyrian army. Because Israel will not repent, the Lord will send Assyria to punish them with conquest and exile. Today we have an example of that in our popular culture that longs to be "bad", and our "heroes" corrupt basic morality. However, if we reject the excuses of pop culture and instead revel in the community of faith, which knows right from wrong, the Lord our Counsel will guide us to true joy and lasting pleasure in goodness of life.
In chapter 6 Isaiah's vision is the climax of his message. This glimpse of God's glory validates his message from God. (I love verse 3 because we sing it frequently in the Divine Service.) The Lord appears to Isaiah and calls him to be a prophet. Isaiah protests that he is a sinner. In our Baptism and through the Word, the Lord calls us too as His messengers. We are to relate to others what we have heard and seen about the Lord. We must not let the shame of past sins silence us. The Lord Jesus has made atonement for us in the tabernacle of God's presence on high. Just as Isaiah was cleansed when the coal from the altar touched his lips, so our Father cleansed us in the waters of our Baptism by joining us to Christ in His death and resurrection. In Christ, He made us new creations who love Him, trust Him, and have His power to live holy lives. We are now His saints, a word that means "holy ones". Yet our old sinful nature still lives in us. It urges us to give into the temptations of the unholy trinity- the devil, the world, and our flesh. We often yield to them, bringing evil into our lives. We often serve ourselves first, trying to please our friends, and attempt to fit into our world, satisfying our urge to seek pleasure and comfort at all costs. We are saints and sinners at the same time.
The chapter in Mark reminds us of Christ's forgiving power. His critics couldn't stand that, but as Peter reminds us in his first letter, though our flesh will perish, the Word of the Lord stands forever. Through faith in the Gospel, we receive the promise of life forever.
Jesus outrages His critics by calling Levi the tax collector to follow Him, then eats with a household of equally "defiled" people. Later they accuse His disciples of violating the Sabbath. Jesus uses the opportunity to claim divine authority and assert His messianic claims. In this chapter we have sinners and we have saint. Which are which? The answer isn't what either group would expect. The tax collectors and prostitutes who followed Christ are saints because they followed Christ. They're still sinners, as we all are until we die, but they are justified by Christ's work, not by any action of their own. The Pharisees are sinners, like we are, but because they don't follow Him, they can't claim the name saint. They falsely believe that following the Law and living the life of a "good Jew" will count for something. Little do they realize it counts for nothing.