Why is the month of Rajab singled out, distant from the Sacred Months?

The sacred months are: Rajab Mudar, Dhu al-Qa'dah, Dhu al-Hijjah, and Muharram. Their mention is found in the Holy Quran and the Prophetic Sunnah.

The wisdom behind the sanctity of these months is that the gravity of sins and acts of obedience are amplified within them. The Arabs, even in the pre-Islamic era, revered them. Some scholars have mentioned that the wisdom behind singling out Rajab is to facilitate 'Umrah in the middle of the year, while the other consecutive months are for Hajj. The distinction of these times may be for wisdom known to Allah, and it could be to increase the impact of obedience on the soul or to deter a person from injustice and disobedience in general.