The Quran

وَإِذ قالَ رَبُّكَ لِلمَلائِكَةِ إِنّي جاعِلٌ فِي الأَرضِ خَليفَةً ۖ قالوا أَتَجعَلُ فيها مَن يُفسِدُ فيها وَيَسفِكُ الدِّماءَ وَنَحنُ نُسَبِّحُ بِحَمدِكَ وَنُقَدِّسُ لَكَ ۖ قالَ إِنّي أَعلَمُ ما لا تَعلَمونَ

Muhammad Asad

AND LO!¹ Thy Sustainer said unto the angels: "Behold, I am about to establish upon earth one who shall inherit it."² They said: "Wilt Thou place on it such as will spread corruption thereon and shed blood - whereas it is we who extol Thy limitless glory, and praise Thee, and hallow Thy name?" [God] answered: "Verily, I know that which you do not know."

The interjection "lo" seems to be the only adequate rendering, in this context, of the particle idh, which is usually - and without sufficient attention to its varying uses in Arabic construction - translated as "when". Although the latter rendering is often justified, idh is also used to indicate "the sudden, or unexpected, occurrence of a thing" (cf. Lane 1, 39), or a sudden turn in the discourse. The subsequent allegory, relating as it does to the faculty of reason implanted in man, is logically connected with the preceding passages.
Lit., "establish on earth a successor" or a "vice-gerent". The term khalffah - derived from the verb khalafa, "he succeeded [another] " - is used in this allegory to denote man's rightful supremacy on earth, which is most suitably rendered by the expression "he shall inherit the earth" (in the sense of being given possession of it). See also 6:165, 27:62 and 35:39, where all human beings are - spoken of as khala'if al-ard.