This poem
First of all, the language is plain and simple, almost rough, without too much text rendering, which is naturally touching.
Secondly, the understanding of the meaning of life is initiated by crying and tears, which is realistic and profound. Although it is similar to the concept of "born with bitterness" in Buddhism, its position is completely different and positive!
The second time, there is the judgment of the value of life, that is, people's evaluation of you. If you make more contributions to mankind, people will shed more tears for you, and tears are pearls praised for you!
The poem also discusses the relationship between happiness and crying. "Cry if you cry", and cry for the country and the people. This is the process of a person's struggle and doing things that are beneficial to the people. So "the time in between is called happiness"