Spiritual warfare, what is it?
The Immaculate Conception is the conception of the Virgin Mary free from original sin by virtue of the merits of her son Jesus. Because we are born with original sin by the fall of Adam and Eve, we have difficulty controlling our flesh impulses by reason and will. Saint Thomas Aquinas in his 'Summa Theologica' book gave us an understanding of what original sin does to us, what is prepared in the afterlife, where we are located in the heavenly realm, etc. We know that Baptism, by imparting the life of Christ's grace, erases original sin and turns a man back towards God, but the consequences for nature weakened and inclined to evil, persist in man and summon him to spiritual battle. Spiritual warfare and exorcism experiences are interconnected. We are constantly tempted until our deaths; demons are everywhere and ever-present in every hate action, anger, and discord. Catherine Emmerich would see Caiaphas (the Jewish high priest plotting to kill Jesus) above hell in his discourse against Jesus. Mary of Agreda's comments on demons plotting against Jesus and Mary are many; to stop human redemption at first, and after being defeated by the crucifixion, demons' effort is now to make people forget about our given redemption, wasting our time on earthly preoccupations, false idols; suggesting erroneous ideas ("Mystical City of God" reference). If we are not suffering any spiritual warfare, we are very likely not going to Church, praying, etc.
Book: The Spiritual Combat (annotated) Scupoli, Lorenzo
Book: Manual for Spiritual Warfare by Paul Thigpen
But let an exorcised demon further clarify spiritual warfare. Advice from a series of compiled exorcisms from 1975 to 1978,
But we say: you shouldn't pray; the more you pray, the more we [demons] will fight against you, because you provoke us. You will have the most beautiful life if you do not pray, if on the other hand, you do your own will... [if you pray] you will have only persecution, you will have only enormous misfortune.
Book: Warnings from the Hereafter to the Contemporary Church: Confessions of Hell, literal text of revelations made by demons during exorcisms by Jean Marty
Saint Thomas Aquinas in 1250 said,
As Hilary says (Super Matth., cap. iii.): "The temptations of the devil assail those principally who are sanctified, for he desires, above all, to overcome the holy. Hence also it is written (Ecclus. 2): Son, when thou comest to the service of God, stand in justice and in fear, and prepare thy soul for temptation."...temptation which comes from the flesh cannot be without sin, because such a temptation is caused by pleasure and concupiscence; and, as Augustine says (De Civ. Dei xix), "it is not without sin that 'the flesh desireth against the spirit.'"...there is no danger in giving the devil such an occasion of temptation; since the help of the Holy Ghost, who is the Author of the perfect deed, is more powerful* than the assault of the envious devil... The temptation which comes from the enemy takes the form of a suggestion, as Gregory says (Hom. xvi in Evang.). Now a suggestion cannot be made to everybody in the same way; it must arise from those things towards which each one has an inclination. Consequently the devil does not straight away tempt the spiritual man to grave sins, but he begins with lighter sins, so as gradually to lead him to those of greater magnitude.
Book: Summa Theologica by Saint Thomas Aquinas
[Mary speaks:] he [the enemy] introduces into the heart the delights of secular songs and of various sweet-sounding instruments, of useless tales and of narrations of the praises of one's own person. The more these things raise one up through pride in oneself, the more distantly one is separated from the humble Christ...for the less costly and valuable his clothes have been, the more lavish shall be his reward. [S.Bridget,1360]
The erroneous concept of reincarnation may be answered by Saint Agustine of Hippo in the year 422,
That these were false recollections, such as those we commonly experience during sleep, when we seem to remember as though we have done or seen something which we have not done or seen at all, and that the minds of those even who are awake were affected in this way by the suggestion of the evil and deceptive spirits, whose care it is to deceive men by confirming or sowing this erroneous opinion about the revolutions of souls, can be conjectured from this...it caused him no embarrasment to hold a belief which would admit the risk of a mother's returning as a girl and marrying her own son.
Book: Augustine: On the Trinity Books 8-15 by Augustine
Why are we tempted in our lives? Let Jesus answer Saint Bridget of Sweden (1303–1373):
Moses did not lead them to the promised land immediately but to the desert,so that they would be tested and instructed there. This is how it is now, for when the people have accepted my faith and my commandments, they are not led into heaven immediately; for it is necessary that men should be tested in the desert - that is, in the world - as to how much they love God... for they love the world and all the things in it more than me, who am their Creator. Therefore, the world is their god, and not I...he wants to have all things without moderation and reason. For, if his bodily nature could bear it, he would without end have sex, drink without restraint, desire without measure and limit, and, as long as he could sin, he would never desist from sin...people want to go to Heaven through their pride, and they do not trust in me but in themselves, doing their own will and abandoning mine...their torment shall be everlasting.They thus hate me like a snake, worship an idol instead of me, long for their own desires more than me, and love their own pride instead of my humility... If bad thoughts did not sometimes get in the way, human beings would be angels and not human, and they would think they got everything from themselves.Therefore, in order that a man might understand his weakness, which comes from himself, and the strength that comes from me, it is sometimes necessary that my great mercy allows him to be tempted by bad thoughts. So long as he does not consent to them, they are a purgation for the soul and a protection for his virtues...still they are very healing for the soul and lead it toward eternal life and toward the kind of health that cannot be gained without some bitterness.
Book: The Prophecies and Revelations of Saint Bridget (Birgitta) of Sweden: Volume 1 by Saint Bridget