Then Salam (peace) to you from those on the right,
meaning, the angels will deliver the good news to them by saying, "Peace be upon you," i.e., be calm, you will be led to safety, you are among those on the right, as Ikrimah said, "The angels will greet him with the Salam and convey to him the news that he is among those on the right."
This is a good explanation, and it conforms with Allah's statement,
إِنَّ الَّذِينَ قَالُواْ رَبُّنَا اللَّهُ ثُمَّ اسْتَقَـمُواْ تَتَنَزَّلُ عَلَيْهِمُ الْمَلَـيِكَةُ أَلاَّ تَخَافُواْ وَلَا تَحْزَنُواْ وَأَبْشِرُواْ بِالْجَنَّةِ الَّتِى كُنتُمْ تُوعَدُونَ
نَحْنُ أَوْلِيَأوُكُمْ فِى الْحَيَوةِ الدُّنْيَا وَفِى الاٌّخِرَةِ وَلَكُمْ فِيهَا مَا تَشْتَهِى أَنفُسُكُمْ وَلَكُمْ فِيهَا مَا تَدَّعُونَ
نُزُلاً مِّنْ غَفُورٍ رَّحِيمٍ
Verily, those who say;"Our Lord is Allah." and then they stand firm, on them the angles will descend (at the time of their death) (saying);"Fear not, nor grieve! But receive the glad tidings of Paradise which you have been promised! We have been your friends in the life of this world and are (so) in the Hereafter. Therein you shall have (all) that your souls desire, and therein you shall have (all) for which you ask. An entertainment from the Oft-Forgiving, Most Merciful." (41;30-32).
Allah's statement,
وَأَمَّا إِن كَانَ مِنَ الْمُكَذِّبِينَ الضَّالِّينَ