Is it true that the rainbow can come only after the rain?

Technically no, but you are observant to notice that after the rain is when they tend to occur. To create a rainbow, you need sun shining on drops of water. read more

No. Rainbows can form before, during, or after a rain, as long as you have sun shining on the raindrops that are 42° away from the point directly opposite the sun, from your perspective. If it is raining to your west close to sunrise, you may see a rainbow to your west, and if it is raining to your east near sunset, you may see a rainbow to your east. read more

It is a metaphor/allegorical phrase that is meant to communicate the idea that after dark experiences/periods of life there is a light one that follows. After bad comes good, essentially. read more