قَالَ وَمَن يَقْنَطُ مِن رَّحْمَةِ رَبِّهِٓ إِلَّا ٱلضَّآلُّونَ

Angels visited Abraham in the shape of human beings. In an exchange of questions and answers, they said that they had come with the command of God. What was this command for which the angels had come to Abraham? This was the good news of an extra-ordinary reward which could not be expected under ordinary circumstances. When God wants to confer an extraordinary benefit on man, He sends His special angel to him in order to accomplish the task. Angels of this kind come to prophets as well as to ordinary mortals. The difference is that when a prophet is visited by angels, he sees them and consciously grasps that those are angels, but ordinary men do not have this kind of certain knowledge or consciousness. However, the close proximity of angels may evoke unusual feelings in him. Such feelings can convey hints of the fact that at that time he is possibly in the company of the special angels sent by God.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (15:56)