I have read that in Islam best women are those who are loving and can have lot of children. I can understand the loving side but women don’t have any control on how many children they can have. Why the women who can have children are superior to women who cannot have children. Prophet (peace be upon him) stopped one of his companions marrying a woman who could not have children and I have also read that Hazarat Umar divorced two of his wives because they were barren. Why are women punished for something which is not under their control? How will they be able get married? It seems that women who cannot have children are sort of outcast as I have read some scholars consider it Mukroh to marry a woman who cannot have children. Why this restriction only applies to women and not men? Men can be infertile too.

All praise be to Allah, and may His peace and blessings be on His last and best messenger, Muhammad and his purified household and honorable companions. It is not true that in Islam the best women are the ones who can bear a lot of children. What is true is that they are the best women to marry, which is common sense, plus it was recommended by the Prophet in the hadeeth you alluded to in which he said; “Marry the compassionate and fertile women…” There is a difference here. It is not a secret that there are qualities other than one’s religiosity and manners that would make him or her a better candidate for marriage such as the appearance, the wealth, and others. That does not mean that prettier people are closer to Allah, for the Prophet said: “verily Allah does not consider your appearances or bodies but your hearts and actions.” The younger man who is about to marry is encouraged to marry a fertile not a barren woman for one of the objectives of marriage is to have children and make a family. That young man is not prohibited to marry a barren woman if he decides to do so, and the Prophet did not prohibit anyone from this, but encouraged them to seek a fertile woman. As for that barren woman, she can be someone’s second wife or marry someone who had children from a previous marriage or someone older or even a younger man if he decided to marry her. Allah knows best.

I am doing a research on Islamic law and I need a clarification on some of the following isues: First: Does the principle of gradual implementation of sharia also apply in cases like theft? Can the leader apply another punishment until his people is well educated islamicly? Second: What is the punishment in cases where retaliation is forbidden,like when a parent kills his child or when a muslim kills a non-muslim? Third: Is the book qawaid al ahkam reliable in the field of law? I heard some scholars praising it and others condemn it.

All praise be to Allah, and may His peace and blessings be on His last and best messenger, Muhammad and his purified household and honorable companions.
As for the issue of gradual implementation of shari’a, it is of the more complex matters to address and must be tackled by the grandest and most trustworthy scholars of Islam so as not to become an excuse for abandoning the shari’a. but, generally speaking the gradual implementation of shari’a is acceptable given there will be no unwarranted delay or deferment of its application in entirety, which is a collective obligation on the ummah.
As for the parent and child and the Muslim and non-Muslim, the punishment will be decreed by the judge to suit the crime. There are disagreements over these rulings between the scholars, and some indicate that if the parent’s killing of the child is known to be intentional and premeditated, then they are killed. The disagreement regarding the Muslim and non-Muslims could be sought in the fiqh books.
As for the book Qawa’ed al-Ahkam by Imam al-‘Ezz, it is one of the greatest books written, yet it must be learned under the supervision and guidance of a true scholar so that one doesn’t get misguided by misinterpreting it. After all, it is about the making of fiqh and objectives of shari’a. One may not perform surgery after reading a book on surgery. Allah knows best.