"'"The silver is mine and the gold is mine," declares the Lord Almighty. "The glory of this present house will be greater than the glory of the former house," says the Lord Almighty, "And in this place I will grant peace," declares the Lord Almighty.'" NIV translation
This passage tells us of the mission of Jesus Christ which was to bring peace to man from God. The Jews were expecting this peace to come from following the religious practices and obeying the Mosaic Law because they did not realize that the law could not bring peace to man. The Jews were looking at the physical building and its furnishings but God was promising them (and us) something much more valuable.
"On the twenty-fourth day of the ninth month, in the second year of Darius, the word of the Lord came to the prophet Haggai: 'This is what the Lord Almighty says: "Ask the priests what the law says: If a person carries consecrated meat in the fold of his garment, and that fold touches some bread or stew, some wine, oil or other food, does it become consecrated?"' The priests answered, 'No.' Then Haggai said, 'If a person defiled by contact with a dead body touches one of these things, does it become defiled?' 'Yes,' the priests replied, 'it becomes defiled.'" NIV translation
On this day (December 24, 520 B.C.), the prophet delivers a message to the priests in the form of questions regarding the law. From these questions, we see that holiness is not transmitted by contact with an object. Just because they passed through the doors of a temple didn't mean that they were holy in God's sight. The same thing is true for us today, in that, just because you enter a "church building" it does not make you a Christian.
"Then Haggai said, 'So it is with this people and this nation in my sight,' declares the Lord. 'Whatever they do and whatever they offer there is defiled.'" NIV translation
Because of their idolatry, their worship was not acceptable to the Lord.
"'Now give careful thought to this from this day on - consider how things were before one stone was laid on another in the Lord's temple. When anyone came to a heap of twenty measures, there were only ten. When anyone went to a wine vat to draw fifty measures, there were only twenty. I struck all the work of your hands with blight, mildew and hail, yet you did not turn to me,' declares the Lord." NIV translation
God tells the people to look around them and remember how things were before this day. He had removed His hand of blessing from them and so they struggled to survive on their own. It is much the same with us before we come to accept the gift of salvation through Jesus Christ. We struggle and struggle to get through the day on our own as God is waiting for us to call on Him.