"And do not weaken and do not grieve," meaning: do not become weak in fighting the polytheists, "while you are the superior ones," meaning: those who are triumphant and victorious, "if you are," meaning: if you are "believers."
﴿وَلَا تهنوا وَلَا تحزنوا﴾ أَي: لَا تضعفوا عَن قتال الْمُشْركين ﴿وَأَنْتُم الأعلون﴾ يَعْنِي: الظاهرين المنصورين ﴿إِنْ كُنْتُمْ﴾ يَعْنِي: إِذا كُنْتُم ﴿مُؤْمِنِينَ﴾