Angels take any form they wish in the physical world. As crystal water takes the form of the cup in which it is poured, angels can take the form of any creation which they visit. They do not retain their full original form of light when they are sent to human beings: "Say: If there were in the earth angels walking secure, We had sent down for them from heaven an angel [without change] as messenger" (17:95). Angels can come as birds, as human beings, or as a form of light like a rainbow adorning the sky. They have a mind and a heart, but no will and no desire other than to serve and obey God. They are never too proud to obey Him.
Angels worship day and night without fatigue. They do not need to sleep, as their eyes never tire. They know no heedlessness. Their attention never wavers. Their food is glorification of God, their drink is to sanctify and to magnify Him. Their intimacy is in calling their Lord through hymning and singing His praise. Their enjoyment is to serve Him. They are devoid of any and all physiological restraints. They suffer no mood-changes.
Angels inhabit Paradise and the seven heavens. They worship more than human beings because they came before them and they have greater and more powerful faculties than they. They are more pious than human beings because they are innocent and unable to fall into mistakes or wrongdoings. They never ask forgiveness for themselves but always for human beings. This shows us how much they care for us and to what extent God created them to look after us. God made them our guardians because a guardian is more perfect than the one he guards.
Angels are more knowledgeable than human beings. The teacher, again, is better than the student. Their knowledge is of two kinds: intellectual and traditional. "Intellectual" means here: "of the essence of reality" or "of the heart." "Traditional" means: "revealed and translated down from above."