Chapter 13: Verse 17 (partial)
The above verse underscores the workings of the universe. We learn from both the Quran and history that whatever is good has an enduring quality. This is an altogether different notion from the survival of the fittest that has gained much popularity in our times.
The Nature of Scum
Whatever is not good or positive or useful and which does not contribute to man's survival or comfort or progress is branded as "scum" by the Quran. As a comprehensive, wide-ranging term this refers to something which is devoid of substance. It lacks stability and constancy. At most, it signifies a sudden, powerful movement which does not have any permanent form. Scum appears at the top, comprising dirt and impurity. It is not of any benefit for mankind. Either it disappears while floating on the top or is relegated to the sides. In either case it does not last. It does not have the capacity for survival.
Allah's law entails that evil or scum cannot flourish for long. Were scum to last, it would pose a danger to the existence of all creatures in the world. By contrast to it is that which benefits mankind and that which lasts on earth.
If Muslims prove themselves as beneficial for their society, they will justify their presence. So doing, they will appear as indispensable. In that eventually they cannot be uprooted by tyranny. Muslims will remain unaffected by their surroundings. Having displayed their mettle, they will be held in high esteem by everyone. Allah has guaranteed the presence and existence of those who are valuable for the cause of true faith.
"Guidance from the Holy Quran" - Sayyid Abul Hassan Ali Nadwi, pp. 221, 222