Spiritual struggle, doing good and leaving the sinful esoteric and exoteric actions, has been alluded to as greater jihad (jihad e akbar) in classical Sufi texts. 

Irrespective of the debate of it being a Prophetic quote (Hadith).  Recently I came across a beautiful explanation. 

Shaikh Sayyid Shabbir Kakakhel (Allah preserve him) said that the greatness here is due to the time involved in it. The jihad (armed struggle) with an enemy is for a restricted period of time and eventually ends. Whereas, the spiritual struggle is a lifelong, daily constant squabble. It ends only with death.  

اندریں راہ می تراش و می خراش

تا دم آخر دمےفارغ مباش

JazakAllah