The older I get the more I see that there are deeper spiritual truths in Christianity than any other religion. When I was younger I felt this but was under the fashionable impression that all religions said more or less the same thing and were just different ways of bringing man to God if one practiced them seriously enough. I still think that's the case (within reason, of course) but I also think that the salvific power of other religions was greatly augmented by the advent of Jesus Christ in this world and the spiritual impetus that advent gave to everything that could receive it. Thus it affected all genuine forms of spirituality and gave them a boost. It is no accident that the Mahayana form of Buddhism postdates Christ, and even Hinduism acquired extra spiritual force from Christ's arrival in this world and the spiritual power he released. This statement is clearly unprovable and would be rejected by Hindus and Buddhists alike but I make it because it seems to me to be the simple truth. It doesn't diminish other religions to say that they stand in the shadow of Christ. They remain what they are which are vehicles given by God, or those that act on his behalf (since God delegates), to helps souls in this world return to their source, but in them all there is still a veil over the fullness of truth. That veil was lifted by Christ. Other religions are effective in their own way but they are incomplete. Only in Christ is the truth made complete.
Apart from the person of Christ, in which all spiritual truth is embodied and through which it stands revealed more clearly than anywhere else, there are two principal teachings in Christianity which take it further than any other form of religion. These are the teachings of the Trinity and the fact that God is Love. You might say that other religions include these but I don't think they do in the same fully comprehensive way. Buddhism has its impersonal compassion but that is rather a mild thing compared to love especially in the context of the denial of the reality of the person. And those who try to force the Buddhist concept of the Trikaya or three bodies of the Buddha into the Christian Trinity are stretching things way too far. Buddhism denies God anyway which is its fundamental flaw. Likewise Hinduism has its trinity of gods in Brahma, Vishnu and Siva as well as the idea of existence as sat-chit-ananda (being-consciousness-bliss) but these have no relation to the Trinity as understood in Christianity as three persons in one God though they might be a reflection or distant echo of that truth. Even Hindu bhakti is not the same as agape in that it is an emotional thing, and love in the Christian sense is not an emotion but an act or condition of being.
My assertion that Christianity contains more of spiritual truth than any other religion might be dismissed as partisan were it not that a spiritually attuned and impartial mind should be able to see that in Christ there is a holiness just not present elsewhere as well as a truth more fully revealed than anywhere else. The light he brought illumined the whole world and spread even where his teachings were not outwardly known. I mean by this that the light of Christ radiated out on a subtle or immaterial level to be picked up by those sensitive enough to respond to it and then interpreted according to their understanding. It is also, as he himself said, through him, and only through him, that all men now reach God even if they do so through another religion than Christianity, which is quite possible. This is an inner truth that can be known in the heart even when not fully accepted by the head.
This truth is also why Christmas is important. The first Christmas was the time when the light of God entered the world. That the light was for the whole world is demonstrated by the visit of the three magi from the East, representing the pinnacle of previous spiritual knowledge, who came to pay their respects to the infant Jesus as the saviour of the world. They were not Jews but they came because they knew that the light embodied in this baby was universal. It repaired the damage done in the past and offered to all men the chance to free themselves from the bondage of matter not by effectively abandoning the relative world of individual beings, of love and beauty and goodness, all of which can only exist in a world of multiplicity and form, for the absolute of pure spirit as taught by the Buddha, but by reconciling the outer and the inner, the relative and the absolute, the One and the Many, through the holy mystery of love. This did not require rejecting suffering as the Buddha had done by rejecting the self that suffered, but fully accepting suffering and offering it up as a sacrifice to God. In this way the fallen self was redeemed and made holy instead of being jettisoned as a burden on existence. Thus was the purpose of creation fulfilled rather than being negated.
So Christmas marks the time when God's reason for creating man is revealed and its fulfilment made possible. And the holy purity of the new born baby reminds us that Christianity goes beyond other spiritual approaches in that it alone fully validates the person, the person that other religions reject as the source of ignorance and a blot on the pure whiteness of naked existence. Of course, even in Christianity the separate self must be given up, as Christ demonstrated at the crucifixion, but what is given up is the false self, the self that by the barriers of its self-centredness blocks out God. The true God-given individuality remains and is then revealed as a shining being of light, a unique son of God born of the holy marriage between Spirit and Matter. And the possibility that we can become this being of light is what Christmas is all about.