From my understanding of "I believe that Jesus was God in the flesh," is a reference to Immanuel."
“Behold, a virgin shall be with child and shall bring forth a Son, and they shall call His name Emmanuel” (which being interpreted is, “God with us”). Matthew 1:23, there is more then just this one verse though, when going on over to read the Gospel of John, which brings forth more of the revelation of whom Jesus is, of course not only being the Word of God, however that by his life, he and his Father were working together, and they were one together in working on reconciling the world back to the way it was prior with everyone having access to Yahava, because of the Son of God, coming and fulfilling the Law, and nailing the old covenant to the cross with a warning that the end was closing which would be the end of that Age.
That is what I think about when I always here that comment though - It's an expression of the Word of God, the Holy Spirit of God, being within the body of the Lord Jesus Christ. The spoken word from Yahava, created light, as Yahava spake to the notion of what was on his heart, to make light, and the the Word from God created that light, in which then Yahava separated it. Jesus was an expressed image of his Father, who was His Son.
There are questions and answers on mainly "If Jesus was God in the flesh, then how could Jesus die" or "If Jesus is God, then how did God die on the cross?"
Naturally that question is understood as it is asked, however by the spirit, and trusting in Yahava to come through in accordance to agape love, there is a reasonable answer and way to explain it. The Word of God never died, the body of Jesus died on the cross. From what you believe from this part here onward I do not know.