Albert Barnes on Matthew 18:10

Take heed that ye despise not one of these little ones, etc. That is, one who has become like little children--or, a Christian. Jesus then proceeds to state the reason why we should not despise his feeblest and obscurest follower. That reason is drawn from the care which God exercises over them. The first instance of that care is, that in heaven their angels do always behold his face. He does not mean, I suppose, to state that every good man has his guardian angel, as many of the Jews believed; but that the angels were, in general, the guards of his followers, and aided them, and watched over them, Heb 1:14.

Do always behold the face of my Father, etc. This is taken from the practice of earthly courts. To be admitted to the presence of a king; to be permitted to see his face continually; to have free access at all times, was deemed a mark of peculiar favour, 1Kgs 10:8, Est 1:14 and was esteemed a security for his protection. So, says our Saviour, we should not despise the obscurest Christians, for they are ministered to by the highest and noblest of beings; beings who are always enjoying the favour and friendship of God.

(f) "angels do always" Acts 12:15 (g) "behold" Ps 17:15