The modern christian does not know the other side of God. He knows so much about the grace and mercy of God but he rarely hears about the wrath and judgement of God yet both sides exist in God. Some may think it is an old testament concept when we talk about God's wrath yet Ananias and Sapphira are examples of what can happen when God want to judge sin.
The idea of preaching and teaching that old testament is not for us and that God in the old testament is not the same as the God in the new testament strips God of his core nature that is revealed all through scriptures.
In the book of Hebrews 12:29, the writer says, "for our “God is a consuming fire". This is the same God we read about in both old and new testament. No difference. The God who judges sin with his wrath in the old still does in the new. Thr writer of Hebrew affirms that.
Talking about the danger of falling away and backsliding, in Hebrews 10:31, the writer says, "It is a terrible thing to fall into the hands of the living God". If it is not terrible, the writer wouldn't have said it by inspiration of the Spirit.
Jeremiah knew all these and that is why he prayed that God should not correct him in anger but gently. Nobody can withstand the anger of God. That is why we must walk with him in fear and reverence. The generation that did not fear God will eventually come under God's wrath.
This is not to scare you or downplay God's mercy. Rather, I don't want us to take His grace and mercy for granted thinking we can always get away with sin. If you realize yourself in this sermon, ask God to forgive you and not correct you in his anger.