"Indeed, Allah and His angels send blessings upon the Prophet," meaning: that Allah forgives the Prophet, and the angels seek forgiveness for him. "O you who have believed, ask [Allah to send] blessings upon him," meaning: seek forgiveness for him, "and ask [Allah to grant him] peace in a worthy manner."
﴿إِنَّ اللَّهَ وَمَلائِكَتَهُ يُصَلُّونَ عَلَى النَّبِي﴾ يَعْنِي: أَنَّ اللَّهَ يَغْفِرُ لِلنَّبِيِّ، وَتَسْتَغْفِر لَهُ الْمَلَائِكَة ﴿يَا أَيهَا الَّذين آمنُوا صلوا عَلَيْهِ﴾ يَعْنِي: اسْتَغْفِرُوا لَهُ ﴿وَسَلِّمُوا تَسْلِيمًا﴾.