@CatholicHere_Hi
Yes,angles are pure spirits but they can take human form ,they are not imaginations, When angels or devils appear to men, they assume human form or some other visible shape. Thus the angels that appeared to the Blessed Virgin and to Zachary assumed human form. The devil that tempted Eve appeared as a serpent.
Even demons are pure spirits. They were angels before they became devils.The word “angel” means messenger, and angels have often been sent by God to make known His will to men. Even the devils do service to God, since God always turns the attacks of the devil to show forth more brightly His own glory.
The angel Raphael accompanied Tobias on his journey. The angel Gabriel was sent to the Blessed Virgin Mary at the Annunciation. Angels appeared to the shepherds at the Nativity. An angel was sent to St. Joseph after the departure of the Magi, and after the death of Herod. Angels appeared to the women at Christ’s sepulcher, and to Mary Magdalene.
Certain angels have special charge of nations, communities, churches, etc.Our Lord Himself several times spoke of angels; especially the guardian angels.