Question: The priest said that Jesus ascended into heaven on the fortieth day and then returned to earth on the fiftieth day as the Holy Ghost - is that right?
Answer: What he meant to say was that God who, in the Person of Jesus Christ, had risen from the dead and ascended into heaven - that same God - returned in the Person of the Holy Ghost at Pentecost. It is wrong to speak of one divine Person changing into another. God existed in the three divine Persons of Father, Son, and Holy Ghost from all eternity, and is unchanging. The idea of God changing from one Person to another or of acting through different but not distinct modalities was known in the third century as "Sabellianism (after its principal exponent) or "Modalistic Monarchism," and was condemned by Pope Saint Callistus I (d. 223).