﴿28﴾ فَأوْجَسَ مِنْهُمْ خِيفَةً قَالُوا لَآ تَخَفْ وَبَشَّرُوهُ بِغُلَآمٍ عَلِيمٍ
The blessed Verse 29 is saying that upon hearing such glad tiding, Sarah, Abraham’s (AS) wife, hastened toward the room with a loud voice (fī sarratin) saying: “How may I conceive a child when I am an old [barren] woman.” Qur'anic exegets maintain that Sarah and Abraham (AS) were ninety five and one hundred and ninety years of age respectively at the time.
The blessed Verse 30 is saying that replying to Abraham’s (AS) wife seized by great surprise and fear, the angles said: “Thus says your Lord. Indeed, He is the All-Wise, the Omniscient,” i.e. he is All-Aware of all good and evil things. The angels might have intended to say that they were on a mission from God Almighty to bear them glad tidings rather than saying something of their own, aiming to make her understand that God Almighty willed to reflect his Omnipotence to the world that whatever He willed would be realized and there was nothing impossible against His Omnipotence. Thus, the angels said: “He is the All-Wise, the Omniscient.” The emphatic conjunction inna (“behold, verily, truly”) indicates that whatever God Almighty wills is based upon His Wisdom and Omniscience as to improving the affairs and vanity may never penetrate his Sacred Divine Presence.