Walk cautiously; the angels are everywhere near at hand, as God has charged them, in all your ways. In whatever small corner you will, in whatever quiet spot, have reverence for your angel. Would you have the audacity to do in an angel’s presence what you would not in my sight? Do you doubt the presence of the angel you do not see? What if you heard? What if you touched? What if you smelled? Note that presence of something is established not only on the basis of sight. Not even all corporeal things are subject to sight. So how far removed from any corporeal sense are spiritual things, which need to be tracked down by spiritual senses? 

If you reflect upon faith, you find positive assent of the presence of angels, proof that they are never absent.