إِلَّا مَنِ ٱرْتَضَىٰ مِن رَّسُولٍ فَإِنَّهُۥ يَسْلُكُ مِنۢ بَيْنِ يَدَيْهِ وَمِنْ خَلْفِهِۦ رَصَدًا
Asad Quran Translation
unless it be to an apostle whom He has been pleased to elect [therefor]:21
and then He sends forth [the forces of heaven] to watch over him in whatever lies open before him and in what is beyond his ken22
Cf. 3:179 - "And it is not God's will to give you insight into that which is beyond the reach of human perception: but [to that end] God elects whomsoever He wills from among His apostles".
For an explanation of this rendering of the phrase min bayni yadayhi wa-min khalfihi (lit., "from between his hands and from behind him"), see note  on 2:255 . In the present context the phrase implies that the very fact of his being graced by divine revelation protects every apostle, spiritually, in all concerns of his life, irrespective of whether these concerns are obvious to him or are beyond his ken.
Malik Quran Translation
except to the Rasool whom He may choose for that purpose, and then He appoints guards, who march before him and behind him,
Yusuf Ali Quran Translation
"Except an apostle whom He has chosen: and then He makes a band of watchers march before him and behind him 5750 5751
Cf. iii. 179, and n. 482. See also last note.
Revelation is not a mechanical or material thing. It has to be safeguarded from being distorted or corrupted by ignorance, selfishness, or the powers of evil. How can its precious and subtle worth and the spiritual safeguards against its misuse by human folly or the perversity of evil be expressed in plain human words? We can imagine a very great treasure, which has to be transmitted. To guard it against evilly-disposed persons, a strong escort is required, to march in front and behind, so as to protect it from all sides. When it reaches its destination, the escort presents its credentials and an Invoice showing the Treasure being transmitted. Then the destined receiver knows that it has come intact and feels satisfied. So about spiritual Revelation. The Prophet recognises the credentials and checks the contents on the tablets of his own heart and insight. He has then no doubt that it is a true Message from Allah, and that those who bring it are the true messengers "of their Lord". A) They: the band of watchers. In "he may know" it is better to construe "he" to refer to the prophet who receives the Message from the "watchers".
Mustafa Khattab Quran Translation
except messengers of His choice. Then He appoints angel-guards before and behind them
Piktal Quran Translation
Save unto every messenger whom he hath chosen, and then He maketh a guard to go before him and a guard behind him
Illa mani irtada min rasoolin fainnahu yasluku min bayni yadayhi wamin khalfihi rasadan