Celsus would also have us to offer first-fruits to demons. But we would offer them to Him who said, “Let the earth bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind, whose seed is in itself upon the earth.” And to Him to whom we offer first-fruits we also send up our prayers, “having a great high priest, that is passed into the heavens, Jesus the Son of God,” and “we hold fast this profession” as long as we live; for we find God and His only-begotten Son, manifested to us in Jesus, to be gracious and kind to us.
And if we would wish to have besides a great number of beings who shall ever prove friendly to us, we are taught that “thousand thousands stood before Him, and ten thousand times ten thousand ministered unto Him.” And these, regarding all as their relations and friends who imitate their piety towards God, and in prayer call upon Him with sincerity, work along with them for their salvation, appear unto them, deem it their office and duty to attend to them, and as if by common agreement they visit with all manner of kindness and deliverance those who pray to God, to whom they themselves also pray: “For they are all ministering spirits, sent forth to minister for those who shall be heirs of salvation.” Let the learned Greeks say that the human soul at its birth is placed under the charge of demons: Jesus has taught us not to despise even the little ones in His Church, saying, “Their angels do always behold the face of My Father which is in heaven.” And the prophet says, “The angel of the Lord encamps round about them that fear Him, and delivers them.” We do not, then, deny that there are many demons upon earth, but we maintain that they exist and exercise power among the wicked, as a punishment of their wickedness. But they have no power over those who “have put on the whole armour of God,” who have received strength to “withstand the wiles of the devil,” and who are ever engaged in contests with them, knowing that “we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.”
Source: Against Celsus (New Advent)