The letters and personal conversations are more very contextual and you may just see contrary statements depending on the person and context elsewhere. Books are more authoritative than the personal conversations and letters. Though in some places even in books, he wrote some things as per some modern surveys he heard if that helps it. And that survey result may not be valid now.
In this purport
The śāstras of the yavanas, or meat-eaters, are not eternal
scriptures. They have been fashioned recently, and sometimes they
contradict one another. The scriptures of the yavanas are three: the
Old Testament, the New Testament and the Koran. Their compilation has
a history; they are not eternal like the Vedic knowledge. Therefore
although they have their arguments and reasonings, they are not very
sound and transcendental. As such, modern people advanced in science
and philosophy deem these scriptures unacceptable.
Because the soul is within the body, the body changes through so many
forms. There is a soul within the body of every living creature,
whether animal, tree, bird or human being, and the soul is
transmigrating from one type of body to another. When the scriptures
of the yavanas — namely the Old Testament, New Testament and Koran —
cannot properly answer inquisitive followers, naturally those advanced
in scientific knowledge and philosophy lose faith in such scriptures.
We have all respect for these great preachers, but we do not require
to study books save and accept for some reference. We must push on our
philosophy how to love God. Our process is simple. These scriptures of
the Buddhists and the Christians may be the words of God, but still
the are not always applicable to us. It is just like a king may give
some rules and regulations for some criminals in prison; but for the
good citizens out of the prison these rules are not necessarily
applicable. So these Christian and Buddhist scriptures were delivered
for a different class of men, and we needn't spend our time in
studying their doctrines. You should read our own books over and over
again and as far as possible do not try to enter into controversy. We
do not concern ourselves with any other religion. Our religion is to
become the servant of the servant of the servant of Krishna.
Regarding Aquarian Gospel of Lord Jesus The Christ, I have taken some
stray extracts just to support our views, but we don't give any
importance to that book. The best thing is that we accept Lord Jesus
Christ as a great devotee of the Lord and the son of God. It is better
not to discuss in any detail about the Christian religion or any other
Some such statements are made equating them to Vaishnavism are more context based than complete truth. It could be just appreciating some common good points that's all.
And also it is result of Bhaktivinoda Thakur's vision to give space for other religions. He wrote books so as to encourage even the followers of other religions. He mixed in his books both badralok bengal renaissance mood and traditional gaudiya vaishnavism. One Krishna Samhita book written by him for example, agrees to all modern indologist theories though in his second publication of the same book, he says that "I have presented the modern conclusions for the benefit of the concerned people"
He writes elsewhere
"The religious principles taught by Mohammed and Jesus Christ are
similar to the religious principles taught by Vaisnava sects. Buddhism
and Jainism are similar to Saiva-dharma. This is scientific
consideration of truths regarding religious principles. Those who
consider their own religious principles as real dharma and others
religious principles as irreligion or sub-religion are unable to
ascertain the truth due to being influenced by prejudice. Actually
religious principles followed by people in general are different only
due to the different qualifications of the practitioners, but the
constitutional religious principles of all living entities are one."
Bhakivinoda is speaking in such a way as to encourage the followers of sectarian doctrines such as Christianity and Islam to give up their limited concepts and recognize real dharma [Vaisnavism]. Bhaktivinoda is not condemning the followers of Vaisnava dharma as sectarian for recognizing that Vaisnava dharma is the eternal function of the soul.
Elsewhere, Bhaktivinoda's opinion is [as stated in Tattva-viveka] that no intelligent person will accept the ideas of salvation thru the birth, death and resurrection of Jesus as Christianity suggests.
He writes there
They said that God created the first jiva and had him stay in a
pleasurable garden with his wife. He was forbidden to eat the fruit of
the tree of knowledge. Following the evil advice of an impious person,
the first beings ate the fruit from the tree of knowledge, thus
disobeying God’s instructions. They then fell from that place into the
world filled with misery. Due to their offense, all living entities
are also offenders from the time of their birth. Not seeing any other
way to eliminate this offense, God Himself took birth amongst human
beings, accepted all the sins of those jivas who took shelter of Him,
and then He died. Those that do not follow Him fall into hell
eternally. Thus God punishes Himself in order to liberate the jivas.
An intelligent person cannot make sense of any of this, ei matati
sahaja-buddhite ayatva kora jay na. To have faith in this mixed-up
religion one must first believe these rather illogical ideas – the
living entity’s life begins at birth and ends at death. Before birth
the jiva did not exist, and after death the jiva will no longer reside
in the realm of material activities. Also only humans have
consciousness and other creatures do not. Only those with minute
intelligence can identify with this (ei visvasati nitanta sankirna
Sometimes mixed logic thinks there are two Gods. Then it thinks there
is a God of spirit and a separate God of matter. The God of spirit brings auspiciousness, and the God of matter brings troubles. A
philosopher named Zarathustra taught this idea: That there is a God of
spirit and a God of matter. In his book Zendavesta he taught that
these two Gods are eternal. The devotees of God have only contempt for
these old speculations. Zarathustra is a very
ancient philosopher. When his philosophy found no honor in India,
Zarathustra preached it in Iran. It was by the influence of
Zarathustra's ideas that Satan, an equally-powerful rival to God, made
his imaginary appearance first in the religion of the Jews and then in
the religion based on the Koran.
He also employed Christian terminology in his one book:
The religion preached by Mahaprabhu is universal and not exclusive.
The most learned and the most ignorant are both entitled to embrace
it. The learned people will accept it with a knowledge of sambandha
tattva as explained in the categories. The ignorant have the same
privilege by simply uttering the Name of the Deity and mixing in the
company of pure vaishnavas. The principle of kirtana invites as the
future church of the world, all classes of men without distinction of
caste or clan to the highest cultivation of the Spirit. This church;
it appears, will extend all over the world and take the place of all
sectarian churches, which exclude outsiders from the precincts of the
mosque, church or the temple.
Noble readers! pardon us for intruding on you with these pages. As
servants of Sri Chaitanya it was our duty to propagate His Supreme
Teachings, and in doing a duty, we are entitled to pardon for any
trouble we have given you. We are natives of Bengal, and in couching
our words in a foreign language, we might have been liable to mistakes
for which you will please forgive us.
You will see another place where he correlates religions in terms of rasas: From Moses to Mahaprabhu
In his Chaitanya Shiksamrita he writes,
Concerning different expressions of reverence, in India, the
worshipper sits on an asana, and after performing nyasa and pranayama
he begins his worship. The Muslim faces towards Mecca and worships
five times a day by bowing down. The Christian kneels down with folded
hands and with humility praises the Lord in either church or house.
Each country has its particular rules concerning, proper dress, food,
purity and impurity. If one examines the different religions, one will
see different rituals. One will also different conceptions concerning
the object of worship. Some people, overcome with devotion in their
hearts, establish the form of the Lord in their soul, in their mind
and finally in the external world. Understanding that the form is
nondifferent from the Lord within, they worship that form. In some
religions, because the greater emphasis on logic, the worshipper
simply forms a conception of God in the mind, and worships it. They do
not accept an external form of God. In reality, however, all these
conceptions are forms of the Lord. According to language differences,
different religions call God by different names. The religions have
different names, and the languages used during worship are also
Because of these five differences, it is only natural that various
religions will appear quite different. However it is improper and
detrimental to argue over these differences. If one goes to someone
else's place of worship one should think, "The people are worshipping
my Lord, but in a different way. Because of my different training, I
cannot quite comprehend this system of worship. However, through this
experience, I can deepen my appreciation for my own system of worship.
The Lord is only one, not two. I offer respect to the form I see here,
and pray to the Lord in this new form that he increase my love for the
Lord in His accustomed form." Those who do not follow this procedure,
but instead criticize other systems of worship and show hatred,
violence and envy, are worthless and foolish. The more they indulge in
useless quarreling, the more they betray the very goal of their
religion. However, one should consider the following point. Though it
is worthless to criticize a difference in religious system, if one
sees a fault, one should not tolerate it. It is beneficial for the
living entities if one attempts to correct the fault in the proper
way. Thus Mahabprabhu, in discussing with Buddhists and
impersonalists, led them to the proper path. The devotees of Lord
Caitanya should always take the Lord's behavior as the proper example
When Kali worship in Bengal was attacked by Dayanand Sarasvati, Bhaktivinoda wrote articles to defend Kali worship.
In one lecture Srila Prabhupada says:
Why one should, Christian, become Hindu, Hindu become Christian? They
should know what is God, what He is, what is his relationship with
God. This Kṛṣṇa consciousness movement is that. It is not a movement
for making Hindus to Muslim or Muslim to Hindus or Christian to Hin...
This is not that movement. They clearly understand this. Therefore
they are following. They are accepting. If I would have preached that
Hindu religion is better than Christian religion, they would have
kicked me out long ago. It is a science; it is a philosophy.
In the introduction to his magnum opus, Systematic Theology, Paul Tillich writes:
Theology moves back and forth between two poles, the eternal truth of
its foundation and the temporal situation in which the eternal truth
must be received. Not many theological systems have been able to
balance these two demands perfectly. Most of them either sacrifice
elements of the truth or are not able to speak to the situation. Some
of them combine both shortcomings.
Regarding pranama mantra of Prabhupada, I think it is referring to Buddhism and Advaita which entered western countries before Vaishnavism.