Celebrations, victory, feasts that are not of the Lord are meaningless. They only provide temporary merriment. It is better to spend that time to be sorrowful, in repentance, in humility – and to acknowledge God’s sovereignty, recognize His authority.
Ever since the Old Testament, God has been telling people to look at the eternal and not the temporal. Long term vs. short term thinking.
With prophecy, the problem is that there will be people who will not believe. Just as how people ignored Old Testament prophecy, there will be people who will ignore New Testament prophecy. And there will be those, like many of us, who waver and sometimes forget. We need to be in step with our God always.