14 Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, 15 and release those who through fear of death were all their lifetime subject to bondage.
All religions need to be accepted as authoritative for them to work. Once a Christian believes in the NT, what is it that they believe to be true? "The Word was with God and the Word was God." "The Word became flesh." What were the writers of the NT trying to say? When they quote Jesus, what was he trying to say? The verse you quoted above says it all. Jesus believed he was coming to conquer Satan and death and pay the penalty for the sins of a wayward people. How did he do that? By rising from the dead. The NT builds him up in such a way that, somehow, he must be God in the flesh to accomplish that.
The Baha'i Faith to be accepted as authoritative cannot have Jesus as God. It can't have him rising from the dead. And, it can't have him being the one and only savior of humankind. They need Baha'u'llah to be God's true messenger for this age to have their laws be accepted and followed. They can't do that if Jesus is who the NT claims him to be. He, essentially, has to be proven false, at least, how Christians interpret him to be as false.
The "school grades" analogy only works on a superficial level. The important doctrines of all the different religions don't agree. They are not stepping stones to the next level. If they were to rather say that all religions had pieces of "truths" but were really man's poor attempt at knowing and explaining the truth, that would be different. But, the don't. They say all these "manifestations" were perfect mirrors and reflected the one true God. None of the religions fall into this grade school pattern. They don't describe one true God. They are all over the place in beliefs.
If such a thing were true, then a Hindu should have become a Jew, who should have become a Buddhist, who should have become a Zoroastrian, to a Christian, to a Muslim, to a Baha'i. And where other religious movements fit in, I don't know? They all seem to be trying to explain the supernatural in a way to get us to believe, to get us to love and respect each other. And in that way, barely, are all religions kind of one, one in purpose. The purpose of getting us to love one another. But, we don't. We argue and fight over what the "truth" is. Unfortunately, for all mankind to come together in love and truth according to the Baha'i Faith, everything you believe in... is wrong.
I know you don't feel it wrong. The foundation of your beliefs comes from the NT. It is what gives you the strength and confidence that what you believe is the truth. The NT tells you that Jesus did rise from the dead and he is real... and he, to you, is God. He said he would send you the Holy Spirit to teach you all things. The NT tells you this Holy Spirit descended at Pentecost. You are born again in the Spirit. And now you are told by a "manifestation" of God that all those things you believe are based on a wrong interpretation? That all those things were only "relative" truths and everything was meant to be taken figurative? It's sad, but if the Baha'i Faith is true, Christians never had anything. Everything they believed in and hoped for is false. If that is so, then not only wasn't Jesus God, but this god that the Baha'is claim is real, I hope, isn't real also. He's a deceiver and game player. He's playing with the hearts of men and women, getting them to commit and believe one thing only to dash their hopes and dreams. What is truth? I don't know. No matter what anyone believes, someone else seems to think their truth is better. Keep believing and living your truth.