‘Jesus answered, “Are there not twelve hours in the day? If anyone walks in the day he does not stumble, because he sees the light of this world. But if anyone walks in the night, he stumbles, because the light is not in him”.'
Here He was basically saying that there is a time when it is right to act, even when it is dangerous to do so, as long as it is in accordance with God's clear prompting. In His case the ‘daytime' was still here (compare John 9:4) and it was not yet the twelfth hour, thus He could safely go forward and would not stumble because He was walking in His Father's light.
But the thought is also being applied to mankind as a whole as a general principle. Those who know and follow Him as the light of the world (John 8:12) will not stumble (unless of course they allow darkness to come because they take their eyes off Him). They will be like those who walk during the light of day. But those who walk in the night, who walk in darkness because their eyes are not on the Light of the world, will stumble constantly because they walk in darkness. They have no light to guide.
There are times when it is day, when God has shown us the way and we can act without fear, and there are times when it is night, and we must act accordingly. In those times we must be cautious. In His case He knows that His timing is right, because He walks under guidance from the One Who is the light of this world, as He is. There are other times, He implies, when it is not right to act so, and only those who walk in darkness will do it. Foolhardiness is never spiritual.
‘The light of this world' may here specifically refer to the sun. But even if it does so, in the spiritual application the One Who is Light (1 John 1:5) is also in mind.
Thus we learn that there are times when it is right to act, and times when it is right not to act. Each of us needs to be sure that we make our decisions in accordance with His enlightening, but we must be careful that it is genuine enlightenment and not just a matter of following our own wishes and ideas. The emphasis is on the need to keep their eyes on the Light Who will guide them on their way.