Adoptionism is an error asserting that Jesus was adopted by God, as God, because of His success in being tested by God by the temptation, and crucifixion. This doctrine states that Jesus did not exist prior to His arrival on earth and that when He was baptized by John at the Jordan river, God gave Jesus the power of miracles and adopted Him as His Son.
Errors like this occur due to a lack of knowledge in simply reading the Bible in its plain revelation and comparing verses of scripture with others who are in like context.
In the chapter: Jesus, the certainty that Jesus was, is, and always will be God, eternally is made certain.
Pope Victor, in 190-198 A.D., condemned this heresy that gained its prominence by Theodotus of Byzantium
Later Versions Of Adoptionism
Pope Leo III, in 798 A.D., at a counsel of Rome condemned this doctrine as heresy.
In Spain the Archbishop of Toledo, and Felix, Bishop of Urgel, brought Adoptionism again to the world in the eight century with a slight variation that Jesus is the Son of God by His dual nature as God and Man, but the man nature of God was adopted by God as His firstborn.