Your aim (reward or punishment) is before you. Behind your back is the hour (of resurrection) which is driving you on. Keep (yourself) light and overtake (the forward ones). Your last ones are being awaited by the first ones (who have preceded).
as-Sayyid ar-Radí says: If this utterance of `Alí (p.b.u.h.) is weighed with any other utterance except the word of Alláh or of the Holy Prophet, it would prove heavier and superior in every respect. For example, `Alí’s saying “Keep light and overtake” is the shortest expression ever heard with the greatest sense conveyed by it. How wide is its meaning and how clear its spring of wisdom! We have pointed out the greatness and meaningfulness of this phrase in our book al-Khasá’is.