I've run across versions of this sentiment quite a bit today:
I still remember the day with a heavy heart, and I pray that as a nation we will do whatever it takes to prevent something like this from happening again.Well, "whatever it takes" is repentance, and for the nation itself to repent not every single citizen has to engage in it, but it should be an observance called by the leader of the nation. Past Presidents have done this on behalf of the nation in times of danger, before sending our troops to war for instance. A day of fasting for our sins as a nation, acknowledging them to Him, with prayer for forgiveness and protection.
Perhaps if enough of the churches had such an observance this would go a long way toward protecting the nation in lieu of a Presidential call, but I haven't heard of this going on in any of the churches.
But people remember it mostly with sadness for the suffering endured that day, and with a sense of righteous indignation, with no acknowledgment that it came from God and was deserved. The enemy is thought of as merely human, as if God could not have restrained them. The solutions thought of are merely human: vigilance, preparedness. Also even calls to pray for the dead, which of course is of no use. But people who don't know God don't know what to do; unfortunately many who do know God also don't, that's the biggest tragedy.
In many of the stories that came out of 9/11 God is shown to have clearly intervened: individuals apparently miraculously helped to safety, kept from going to work that day and so on. God intervened in the downing of the plane in Pennsylvania that was aimed for the White House. God has mercy in the midst of judgment.
But overall His hand of judgment has been more and more upon the nation since 9/11. The increase in the presence and status of Islam in this nation is truly astonishing considering that it was Islamic militants who attacked us on 9/11. That's God's judgment right there. We now have a Marxist in the White House who courts Islam. That's God's judgment. The White House didn't need to be physically destroyed; it's being spiritually destroyed.
We've abandoned our Christian roots. I don't care how much people say this isn't a Christian nation or never was, there is a way that is true but a much much bigger way it is not true. The Christian influence in the institutions of the government at the beginning was enormous. Many of the few dozen founders were genuinely Christian. Others who were Deists were serious Deists, serious Unitarians, and they included church services even as part of a day of government business. It shouldn't be so glibly said we're not a Christian nation with that in our background, but it also shouldn't be so glibly said that we are, because Deism/Unitarianism is not Christianity, and apostasy in our leaders would necessarily have contributed to the seeds of our ultimate judgment.
We are no longer Christian even in the sense they used to be, so we probably can't have a day of repentance on that assumption any more. Obama wouldn't recognize the idea anyway, or he'd put a Marxist twist on it and any fast he'd call I'm afraid I would not be able to support.
But a genuine fast and repentance before God is the only thing that would save the nation. Except Christians separately or whole churches uniting in repentance and prayer on behalf of the nation.