‘The day of the Lord’ is a signpost term telling us that this is a Messianic prophecy. This prophecy would not have been welcome for most of the Jews, because they liked to think that day of the Lord would be a time of national blessing and prosperity, but it turned out to be the opposite.
These are predictions of Christ and his church, but at the same time the chapters are interspersed with attacks and viciousness. Will this literally happen to the church, and to the children of the church? No, it is Old Testament language used to describe a spiritual battle finding its fulfilment in New Testament times. But it is important to look at it, and to be a little shaken by it, because, although this will not literally describe what happens to the church, it will be a good figure for the attacks of Satan. He is vicious and the demons of darkness are vicious, and if I go out tomorrow, at the beginning of the day, relaxed and casual and unthinking, and without a prayer of preparation and without readiness for temptation, for ill-temper to strike, or hostile responses to things that may come to me; if I go out completely relaxed to live the Christian life on autopilot, I shall fall, and be brought down, and be easy prey for the devil. That is what this powerful language is telling us. There is going to be a battle: Christ will come, redemption will come, a fountain will be opened all sin and uncleanness, wonderful things will happen, interspersed with attacks launched against Jerusalem, against the truth, against the Lord's people, against the church. But it is all describing New Testament experiences in Old Testament language, and we have to be ready for it, and it makes us much more careful and realistic. We are Christians, we will be defended and helped, but we have to be alive to it.