النُّطفة (sperm-drop): It is the drop of the liquid which brings the spermatozoon which the human being comes from.
As we know, the sperm-drop is a small insignificant thing which is of no value. However, it is of the Power of Allah (swt) that this small insignificant thing is made into a proportionate creation which is great structurally and miraculous in its creation. If every human being was to look at his origin, he would never be arrogant.
فقدّره (destined for him): That is, Allah (swt) destined everything in it with due measure, precision and exactness. Allah (swt) has predetermined each human being’s characteristics, appearance, colour, instincts and feelings. He has also predetermined every organ in him and also every single one of his atoms.
Amazingly, this precision and exactness in the creation of this being is seen in this small insignificant thing which cannot be seen by the naked eye and it is seen, as well, in the great celestial bodies. It is of the blessings of Allah (swt) on us that He has pointed out to us the origin of creation when He (swt) asked this question. He did not leave anyone to answer it but rather, answered it Himself.