Haggai 1: 2-5
When we procrastinate, we are sinning because as James 4:17 says, we know what ought to be doing, but choose not to do it. The Israelites knew that after they rebuilt the walls of Jerusalem under Nehemiah, they were to rebuilt the temple, but they put it off for fifteen years. Our reasons might seem valid to us, but if God has given us the opportunity to do something we may be missing that chance, or even harming our spiritual life in the process.
It had been 15 years since they had returned to Jerusalem and rebuilt the wall under Nehemiah's leadership. They were suffering because they had not followed God's instruction to also rebuild the temple. Much like our current situation in the world today, they were too concerned with pleasing themselves and those around them instead of putting their faith where it belongs... in God who had seen them through so many other trials.