Why do many of those serving in a foreign - language field find it beneficial to study regularly in their mother tongue?
فَلِكَيْ يُحَافِظَ عَلَى صِحَّتِهِ ،‏ عَلَيْهِ أَنْ يَأْكُلَ بِٱنْتِظَامٍ وَجَبَاتٍ مُغَذِّيَةً .‏