from al-'alaa ibn ziyaad who said:
a man asked 'abdullah ibn 'amr ibn al-'aas, saying: which of the believers is best in his islaam? he replied: he from whose tongue and hand the muslims are safe. he asked: then what is the best jihaad? he replied: he who strives against his own self and desires for allaah. he asked: then which of those who migrates (performs hijrah) is best? he replied: he who strives against his own self and desires for allaah. he asked: is it something you have said o 'abdullah ibn 'amr, or allaah's messenger (salallaahu 'alaihi wa'sallam)? he said: rather allaah's messenger (salallaahu 'alaihi wa'sallam) said it.
so striving against ones own self is one of the highest and most valuable means of increasing ones eemaan and causing the servant to draw closer to his lord, the one free of all imperfections. concerning this he the blessed and most high says:
"as for those who strive hard in us (our cause), we will surely guide them to our paths (i.e. allaah's religion)"
so a muslim's striving against his own self and his desires causes his spirit to rise higher, his eemaan to increase and his soul to become purified. furthermore this striving crowns the muslim with a very great crown worn in his life, which is:
12.reported by ibn nasr al-marwazee in ta'zeem qadris salaat (no. 639)
13.soorah al-ankaboot (29):69