In all our dealings with one another we are to reveal Christ. Thus we shall show that we have a genuine connection with the Saviour. God is to receive all honor, all glory. When Christ shall appear, those who are united with Him by living faith will be acknowledged by Him. He will not be ashamed to call them brethren...
The Lord, He is God, and beside Him there is none else. When Satan can bring his craftiness to bear on human minds, deceptive influences are received [as] from heaven. If his deceptions are allowed to enter, many souls will be ensnared by them, before it is seen that they are not from God, but from the enemy of all righteousness.
I assure you that it will be one of our perplexities to distinguish the genuine from the spurious. Deception steals in unawares, just as it stole into the heavenly courts. Satan sought to undermine the confidence of the angels in God’s government. He desired the place occupied by Christ, having it in his mind, that if he gained this position, to make an effort to take the place of God. Adroitly he presented his suggestions to the angels, and many of them received these suggestions. He left his insinuations in their minds to develop. They, not as cautious as their leader, began to communicate their new theories. Satan was the originator of the doubts that they expressed, but he presented them as the opinions of a large number of the angels, and as such, something that should be considered.
Today, Satan works with deceptive guile to captivate human beings by his deceptive theories. The warning to beware of allowing him to enter comes sounding down along the line to our time.
Let none suppose that because they have been used as the Lord’s instrumentalities, they are all-sufficient. The Lord uses men and honors them by giving them His wisdom, as long as they are true to Him, and do not gather glory to themselves. Those who take themselves out of the Lord’s hands, and think themselves capable of managing the work, are not led by His Spirit, but by “another spirit.” Satan steps in, and they change leaders. Then comes the crookedness and subtlety of the serpent’s guile.—Manuscript 37, May 1, 1903, “Directions for Work.”
Reference: E.G. White, "The Upward Look," p. 135