The European farmer grows grass in summer to give his cattle in winter. But this grass has to be. Hence every hour of sun shine is very important for the farmer; he has to be quick. So the proverb means to make the best of a chance and not to let a favorable opportunity slip by. There is a time of everything.
If a man loses that moment, he is put into troubles. Time once past can never be recalled. A blacksmith who never strikes while the iron is hot cannot make anything. If you have something in hand, wait for the proper time.
When the proper time comes, never lose a moment and try to avail yourself of that opportunity. Not to attack when the time is ripe, not to work when the time is enough causes failure in live. In recent space-research, timing is an important factor. One minutes delay may be fatal to the whole plan. The same thing applies to life in general. Life is short and time is fleeting.
Every beat of our heart is taking us nearer our grave. All the time we are losing our faculties. If we fail to do our duty during that limited time, we are doomed. Life, like the weather is uncertain. Sunshine is a youth of our life. If we fail to win great achievements in our young age, we have wasted it. No man can tell when the sun may go behind the clouds; no man can tell when he may die. Hence the importance of every moment of life. Youth comes but once and opportunities never repeat themselves.