His saying: "And when you are greeted with a greeting, greet with one better than it or return it." The greeting is the salutation [Salam]. The meaning of "better than it" is: if a man says, "Peace be upon you," one responds to him with, "Peace be upon you and the mercy of Allah," and if he says, "Peace be upon you and the mercy of Allah," one responds to him with, "Peace be upon you, the mercy of Allah, and His blessings."
And the meaning of "or return it" is: return the greeting to him similar to what he greeted with; and this applies when a Muslim greets you. "Indeed, Allah is ever, over all things, an Accountant [Hasib]." Muhammad said: It means: a reckoner, according to the statement of some of them. [Verse 87]
قَوْله: ﴿وَإِذَا حُيِّيتُمْ بِتَحِيَّةٍ فَحَيُّوا بِأَحْسَن مِنْهَا أَو ردوهَا﴾ التَّحِيَّة: السَّلَام، وَمعنى: ﴿أحسن مِنْهَا﴾ إِذَا قَالَ الرجل: السَّلام عَلَيْكُم، رد عَلَيْهِ: السَّلام عَلَيْكُم وَرَحْمَة الله، وَإِذا قَالَ: السَّلام عَلَيْكُم وَرَحْمَة الله رد عَلَيْهِ: السَّلام عَلَيْكُم وَرَحْمَة الله وَبَرَكَاته.
وَمعنى: ﴿أَو ردوهَا﴾ أَي: ردوا عَلَيْهِ مثل مَا يسلم؛ وَهَذَا إِذا سلم عَلَيْك الْمُسلم. ﴿إِنَّ اللَّهَ كَانَ عَلَى كل شَيْء حسيباً﴾ قَالَ مُحَمَّد: يَعْنِي: محاسبا؛ فِي قَول بَعضهم. [آيَة ٨٧]