Thank you for the question. I personally see that passage in a different light, I do not see it was offered in the light as an eternally exclusive statement, but applicable to a each 'Day of God'. There was also made at that time many promises yet to come.
I see this passage explains the station of the Messenger, and the Claim current amongst humamity. When the Message was given, it was to that Mediator, Jesus we were to turn and to no other. The requirements for that age were given by God through the Mediator, then known as Jesus, Annointed of the Holy Spirit. Baha'u'llah has explained this in great detail now.
There are important considerations we need to identify in the verse you have quoted. The verse is saying Jesus was Christ, Christ is not a surname, it is the station of the Mediator, it means Annointed One, annointed of the Holy Spirit.
This is important, because when Jesus asked Peter who he thought Jesus was, Peter replied that you are Christ. This is that verse.
"... Who do you say I am?" Simon Peter answered, "
You are the Christ, the Son of the living God." Jesus replied, "Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven..."
Now we can use logic. Jesus said the flesh amounts to nothing and it is the Sprit that is the light and life. The Father is not Jesus as the verse shows the Father was in Heaven and we know the Father was yet to come. The Father is of the same Holy Spirit and thus Jesus could offer as the Christ, that the Father and I are One.
Baha'u'llah wrote to the Pope and offered this,
"O POPE! Rend the veils asunder. He Who is the Lord of Lords is come overshadowed with clouds, and the decree hath been fulfilled by God, the Almighty, the Unrestrained… He, verily, hath again come down from Heaven even as He came down from it the first time. Beware that thou dispute not with Him even as the Pharisees disputed with Him (Jesus) without a clear token or proof.... The Word which the Son concealed is made manifest. It hath been sent down in the form of the human temple in this day.
Blessed be the Lord Who is the Father! He, verily, is come unto the nations in His most great majesty. Turn your faces towards Him, O concourse of the righteous… This is the day whereon the Rock (Peter) crieth out and shouteth, and celebrateth the praise of its Lord, the All-Possessing, the Most High, saying: ‘
Lo! The Father is come, and that which ye were promised in the Kingdom is fulfilled!…’ My body longeth for the cross, and Mine head waiteth the thrust of the spear, in the path of the All-Merciful, that the world may be purged from its transgressions…."
Bahá'í Reference Library - Proclamation of Bahá’u’lláh, Pages 83-86
Much can be discussed if you so choose to.
Regards Tony