Islamic teachings and beliefs are of various kinds. Some are called ta`abbudi matters which signify that the orders and commands that Muslims should follow even if the text itself is silent regarding the wisdom behind them.
However, Muslim scholars may perform ijtihad to know some possible wisdoms behind such matters. But the Muslim has to follow them in total and complete submission to the will of the Creator, Allah. For example, the issue of performing some prayers loudly and others silently. Some scholars say that the wisdom behind this is that the night prayers are to be performed loudly and the day prayers are to be performed silently because Muslims were at the early days of Islam and there were fears during the day to be heard by Non-Muslims. However, no one can assure that this is the divine reason behind this legislation.
All in all, the Muslim has to follow and totally submit himself to the divine ta`abbudi order even if he did not grasp its divine wisdom. Other kind of its teachings is based on clear wisdom that is stated clearly in the texts of the Qur’an and Sunnah. For example, Almighty Allah says, “They question thee (O Muhammad) concerning menstruation. Say: It is an illness, so let women alone at such time and go not in unto them till they are cleansed. And when they have purified themselves …” (Al-Baqarah 2: 222) So, the divine wisdom behind the prohibition of having intercourse with a menstruating wife is to avoid its harm. Moreover, some scholars may maintain such a divine wisdom by proving the harm that results if a husband makes love with his wife during menstruation by modern scientific conclusions.