The Quran

وَالَّذينَ هاجَروا فِي اللَّهِ مِن بَعدِ ما ظُلِموا لَنُبَوِّئَنَّهُم فِي الدُّنيا حَسَنَةً ۖ وَلَأَجرُ الآخِرَةِ أَكبَرُ ۚ لَو كانوا يَعلَمونَ

Muhammad Asad

NOW as for those who forsake the domain of evil¹ in the cause of God, after having suffered wrong [on account of their faith] - We shall most certainly grant them a station of good fortune in this world:² but their reward in the life to come will be far greater yet. If they [who deny the truth] could but understand³

For an explanation of this rendering of alladhina hajaru, see surah 2, note 203, and surah 4, note 124. That the "forsaking of the domain of evil" has here a purely spiritual connotation is obvious from its juxtaposition with the "denial of the truth" referred to in the preceding verses.
See note 28 above.
The verb 'alima, which primarily denotes "he knew", has also the meaning of "he came to know", i.e., "he understood"; and since - as pointed out by Baghawi, Zamakhshari and Razi - the pronoun "they" in the phrase law kanu ya'lamun relates to the deniers of the truth spoken of in the preceding passages, the rendering "if they could but understand" is here clearly indicated - the more so as it provides a self-evident connection with the subsequent, objective clause.