Why do we liken a person of extreme kindness to angels?

There is no need to exert oneself in searching for the reasons behind common sayings among people. Instead, one should reflect upon the texts of revelation and busy oneself with the wisdom and benefits contained therein. People's saying about someone that he is an "angel" likely means that they intended to describe his goodness and uprightness. They likened him to angels, who do not disobey Allah and do whatever they are commanded. They are: "Nay, but they are honoured servants, They speak not until He has spoken, and they act on His command. He knows what is before them and what is behind them, and they do not intercede except for those whom He approves, and they are in awe from fear of Him." And "And those who are with Him are not too proud to worship Him, nor do they weary. They glorify Him night and day; they do not flag."