"But he has not attempted the steep path," meaning: he did not attempt the steep path. This is a statement of fact, meaning: that he did not do it.
Muhammad said: The Arabs say, 'la fa'ala' (he did not do) in the sense of 'lam yaf'al' (he did not do).
﴿فَلَا اقتحم الْعقبَة﴾ أَيْ: لَمْ يَقْتَحِمِ الْعَقَبَةَ، وَهَذَا خَبَرٌ، أَيْ: أَنَّهُ لَمْ يَفْعَلْ.
قَالَ مُحَمَّدٌ: الْعَرَبُ تَقُولُ: لَا فعل بِمَعْنى لم يفعل.