"One Lord, One faith, One baptism;" Ephesians 4:5

"But to us there is but one God, the Father, of whom are all things, and we in him; and one Lord Jesus Christ, by whom are all things, and we by him." 1 Corinthians 8:6

Matthew Henry's Concise Commentary

There is no proof of ignorance more common than conceit of knowledge. Much may be known, when nothing is known to good purpose. And those who think they know any thing, and grow vain thereon, are the least likely to make good use of their knowledge. Satan hurts some as much by tempting them to be proud of mental powers, as others, by alluring to sensuality. Knowledge which puffs up the possessor, and renders him confident, is as dangerous as self-righteous pride, though what he knows may be right. Without holy affections all human knowledge is worthless. The heathens had gods of higher and lower degree; gods many, and lords many; so called, but not such in truth. Christians know better. One God made all, and has power over all. The one God, even the Father, signifies the Godhead as the sole object of all religious worship; and the Lord Jesus Christ denotes the person of Emmanuel, God manifest in the flesh, One with the Father, and with us; the appointed Mediator, and Lord of all; through whom we come to the Father, and through whom the Father sends all blessings to us, by the influence and working of the Holy Spirit. While we refuse all worship to the many who are called gods and lords, and to saints and angels, let us try whether we really come to God by faith in Christ.

Satan and Fallen Angels vs. The Christian

The Church at present is in conflict with 'principalities and powers,' with 'the rulers of the darkness of this world,' with 'wicked spirits in high places.  Nothing less truly invulnerable than the whole armor of God can therefore sufficiently protect us against the approaches of such a subtle foe.

Consider, first, that to the devil is ascribed by God Himself the agency of man's apostasy from his Creator. The serpent is said to have 'beguiled" our first mother by his subtlety. Is he less subtle now? And is he likely to be less successful when he has to deal, not with unfallen, but with sinful men? If by his craft he was victorious when he approached the ' image of God'  in the creature, shall he not with even less artifice prevail against those in whom, when he comes, instead of finding 'nothing,'he finds his own likeness?

For what is holiness but likeness to God, and what is sin if not 'of the devil' ? How great the peril, then, of that heart which sleeps in security, and, through ignorance or disbelief in his personal influence, watches not for the footfall of the tempter! Hence that Divine precept to the Church, ' Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour.' 

Again, Holy Scripture plainly teaches that Satan comes to harass and perplex where he knows he cannot destroy. Did he expect, for instance, to prevail when he met the sinless Son of Man in the wilderness? Had he forgotten that terrible sentence which at the beginning was spoken to him by Jehovah Himself, who then put it into that very Bible, 'It shall bruise thy head, and thou shalt bruise His heel'? No, however, while he knew that he could not bruise the Head in the head, yet he knew it was granted him to attack the Blessed One as being a partaker of 'the flesh and blood ' of the children.'' He could not destroy; he would therefore 'afflict' the Righteous One! So, is it still with 'the brethren.' Satan full well is aware of their security and final triumph in Christ, as the redeemed of His blood and the subjects of the indwelling Holy Spirit; he will therefore inject the  poison of doubt and fear into their souls. 

The Personality of Satan part 2

The same Divine authority has caused to be put on record not only the fiery ordeal of personal conflict with him in the wilderness for forty days and nights, but also numerous other instances of terrible engagements between the saints and the great adversary.  With all these and many more such proofs of external evil influence directly exercised on us, how is it possible to confound the personalty of Satan with the principle of evil in the fallen nature of man? 

Yet, if any would even still object, what shall be said of such plain passages as the following ?—

'And the great dragon was cast out, that old serpent, called the devil, and Satan, which deceiveth the whole world; he was cast out into the earth, and his angels were cast out with him.''

'Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh his own; for he is a liar, and the father of it.'

'But some of them said, He casteth out devils through Beelzebub, the chief of the devils' 'If Satan cast out Satan, he is divided against himself; how shall then his kingdom stand ?'

'Thou believest that there is one God; thou doest well; the devils also believe and tremble.'s

'He said unto him, Come out of the man, thou unclean spirit. And He asked him, What is thy name? And he answered, saying, My name is Legion; for we are many.'

'Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels.'

"God spared not the angels that sinned, but cast them down to hell."

'Satan stood up against Israel, and provoked David to number Israel.'

'When any one heareth the word of the kingdom, and understandeth it not, then cometh the wicked one, and catcheth away that which was sown in his heart.'

'In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious Gospel of Christ, who is the image of God, should shine unto them.'

'He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil! 
'That through death He might destroy him that had the power of death, that is the devil! 

Here are many proofs, all going to enforce the solemn point in hand—namely, that there are in existence upon earth a multitude of mysterious beings, called by the Spirit of truth by various titles and names, whose nature is wholly evil, and who, actuated by feelings vindictive towards God and man, are actively engaged in opposing the glory of God and the well being of the human family; and further, that this evil angel host is presided over by a chief, whose present territory is the wide world of the heart of man, and who aims at pressing every event and circumstance of human life into his fiendish service.

The Personality of Satan

It must here be observed,  in spite of all the attempts of unbelievers to disprove the personal existence of the devil, and. to make out that only the spirit or principle of evil is intended by the title, that every quality, every action, which can indicate personality, is attributed to him by the Holy Ghost in the Word of God, and in language which by no rules of fair interpretation can be explained away.

The revelation of the existence of the great Evil Spirit, like every other fact divinely made known in Scripture, was progressive. On the first entrance of evil into the world, the temptation of man is referred only to the Serpent. Throughout the patriarchal and Jewish dispensations only a vague and imperfect revelation of the source of evil was prevalent. Here and there during the succeeding ages we meet with direct references of evil to the influence and instigation of Satan. 

It may here be mentioned that the word Satan primarily means 'adversary', and as a proper name or title it is used in the Old Testament only eight times. In the New Testament, however, the veil is boldly lifted, and the awfully real character of the Prince of this World is constantly dwelt upon. From 'the beginning of the Gospel,'' when the devil appears as the personal tempter of our Lord, through all the Gospels, Epistles, and the Apocalypse, we meet with constant revelations of the personality, origin, power, cruelty, malignity, and final doom, of 'the prince of the demons.'

The complex and vast character of the kingdom of the devil is sufficiently implied in the New Testament by the titles and names which the Holy Ghost has seen fit to employ when speaking of this great fallen spirit. Thus, though not exhaustively, 'Abaddon ' (or Perdition); 'the Accuser of the Brethren ;'4 the 'Adversary ;' s the 'Angel of the Bottomless Pit;' 'Apollyon '(or he that exterminates); 'Beelzebub;' 'Belial'; the 'Dragon'; the 'Father of Lies ;' 3 the 'Great Red Dragon;'4 the'Liar ;'the 'Man murderer;' the 'Power of Darkness;' the 'Prince of this World'; the 'Prince of the Devils'; the 'Prince of the Power of the Air;' 'the 'Ruler of the Darkness of this World' (rather, of this Age); the 'Serpent; 'the 'Spirit that now worketh in the children of disobedience;'the 'Tempter ;' the 'God of this World ;'the 'Unclean Spirit;' and the 'Wicked One.

His character is spoken of by the same Spirit of truth as being presumptuous, proud,  powerful,  wicked,  malignant, subtle, deceitful, fierce, cruel, always active in doing and promoting evil, and yet cowardly.  He is compared to a Fowler employed in setting snares for runaway souls ; to a wicked sower who by night scattered tares among the good seed of the field ;to a wolf, whose nature is to ravage the flock ; and to a lion restlessly wandering about for prey. Against his treacherous and insinuating approaches the Word frequently exhorts the saints to watch and pray. To his sinful solicitations Christ has commanded His disciples to give the most uncompromising resistance.

01 Lester Sumrall - Alien Entities 01 WOF

Derek Prince - Spiritual Warfare 1 of 9 War In Heaven And Earth - Part 1

The Effects of Being filled with the Spirit

1. It is the secret of holiness. There is a measure of the Holy Spirit's life in every regenerate soul, but it is when every part of our being is filled with His love and possessed for His glory that we are wholly sanctified, and it is this divine fullness which excludes and keeps out the power of sin and self, even as it was the descending cloud upon the tabernacle which left no room for Moses within.

Would you have continual purity of heart and thought and feeling, and entire conformity to the will of God? "Be filled with the Spirit;" "Of his fullness have we received, even grace for grace." Let the heavenly water flow into every channel of irrigation and by every garden bed and plant, until all the graces of our Christian life shall be replenished by His grace, and bloom like the garden of the Lord. Only abide in Him and have His abiding, and you shall bring forth all the fruit of the Spirit.

2. It is the secret of happiness. A heart half full is only full enough to make it conscious of its lack. It is when the cattle are filled that they lie down in the green pastures. "These things have I spoken unto you that my joy might remain in you and that your joy might be full."

3. It is the secret of power.  Only full hearts accomplish effectual work for God. Only the overflow of our blessing blesses others.