A watchman in a tower has a vantage point where he can see much further than those on the ground. He can therefore see things that may be coming more easily. That's the whole point: so he can raise the alarm and those on the ground can prepare before the threat arrives. It would be foolish for those on the ground to ignore such a warning just because they can't see the threat. God has set watchmen over us. They are prophets, apostles, church leaders, and even members of our own families when acting upon inspiration from the Lord. The threat of the adversary is very real, and so the true servants of the Lord will never cease warning of the evils of the day. It is up to us to head the warning.