The Father Informed Lucifer that Christ Was His Only Begotten Son 

Satan was well acquainted with the position of honor Christ had held in Heaven as the Son of God, the beloved of the Father. — {RH March 3, 1874}

[Lucifer’s] beauty was so highly exalted that he thought he should be as God, and Christ must be second to him; but the Lord informed Satan this could not be possible. Christ was His only begotten Son. — {Letter 157, 1910 25LtMs, Lt 157, 1910, par. 7}

At the birth of Jesus, Satan knew that One had come with a divine commission to dispute his dominion. He trembled at the angel's message attesting the authority of the newborn King. Satan well knew the position that Christ had held in heaven as the Beloved of the Father. That the Son of God should come to this earth as a man filled him with amazement and with apprehension. He could not fathom the mystery of this great sacrifice. His selfish soul could not understand such love for the deceived race. — {DA 115, 1898}

Pride will never be admitted into heaven. Can we cherish envy in our hearts and yet be found in the kingdom of God?—No; envy cannot be transplanted into the kingdom of God. Satan originated this terrible evil, and its result was that Satan desired and sought to take the place of the only-begotten Son of God. It was because he could not have the place of Christ that Satan revolted in heaven. — {ST February 5, 1894, par. 3} 

There are many of us who have a nominal faith, but we do not bring that faith into our character. The statement is made that the devil believed and trembled. He believed that Christ was the Son of God while he was in heaven; and when upon this earth he was in conflict with Him here on the field of battle, he believed on Christ; but could this save him? No, because he did not weave Christ into his life and character. — {4LtMs, Ms 5, 1886, par. 10}

Who is this that was to come to our world and become incarnate? The only begotten Son of God. “Forasmuch then as the children are partakers of flesh and blood, he also himself likewise took part of the same, that through death he might destroy him that had the power of death.” [Hebrews 2:14.] “The Lord possessed me in the beginning of his way, before his works of old,” Christ says. “When he gave to the sea his decree that the waters should not pass his commandment: when He appointed the foundations of the earth: Then was I by Him, as one brought up with him: and I was daily his delight, rejoicing always before him.” [Proverbs 8:22, 29, 30.] But Christ humbled Himself to come to this earth. This was the hiding of His glory. — {13LtMs, Ms 37, 1898, par. 13}