Until every soul is freely permitted to investigate every book, and creed, and dogma for itself, the world cannot be free. Mankind will be enslaved until there is mental grandeur enough to allow each man to have his thought and say. This earth will be a paradise when men can, upon all these questions differ, and yet grasp each other's hands as friends. It is amazing to me that a difference of opinion upon subjects that we know nothing with certainty about, should make us hate, persecute, and despise each other. Why a difference of opinion upon predestination, or the trinity, should make people imprison and burn each other seems beyond the comprehension of man; and yet in all countries where Christians have existed, they have destroyed each other to the exact extent of their power. Why should a believer in God hate an atheist? Surely the atheist has not injured God, and surely he is human, capable of joy and pain, and entitled to all the rights of man. Would it not be far better to treat this atheist, at least, as well as he treats us?Christians tell me that they love their enemies, and yet all I ask is—not that they love their enemies, not that they love their friends even, but that they treat those who differ from them, with simple fairness.We do not wish to be forgiven, but we wish Christians to so act that we will not have to forgive them. If all will admit that all have an equal right to think, then the question is forever solved; but as long as organized and powerful churches, pretending to hold the keys of heaven and hell, denounce every person as an outcast and criminal who thinks for himself and denies their authority, the world will be filled with hatred and suffering. To hate man and worship God seems to be the sum of all the creeds.

~ Robert G. Ingersoll

As for the negation of the Christian Trinity in the Quran - and this negation is extrinsic and conditional - we must take account of certain shades of meaning. The Trinity can be envisaged according to a vertical perspective or according to either of two horizontal perspectives, one of them being supreme and the other not. The vertical perspective- Beyond-Being, Being and Existence - envisages the hypostases as descending from Unity or from the Absolute - or from the Essence it could be said - which means that it envisages the degrees of Reality. The supreme horizontal perspective corresponds to the Vedantic triad Sat (supraontological Reality), Chit (Absolute Consciousness) and Ananda (Infinite Beatitude), which means that it envisages the Trinity inasmuch as It is hidden in Unity(1). The non-supreme horizontal perspective on the contrary situates Unity as an essence hidden within the Trinity, which is then ontological and represents the three fundamental aspects or modes of Pure Being, whence the triad : Being, Wisdom, Will (Father, Son, Spirit).Now the concept of a Trinity seen as a deployment (tajalli) of Unity or of the Absolute is in no way opposed to the unitary doctrine of Islam ; what is opposed to it is solely the attribution of absoluteness to the Trinity alone, or even to the ontological Trinity alone, as it is envisaged exoterically. This last point of view does not, strictly speaking, attain to the Absolute and this is as much as to say that it attributes an absolute character to what is relative and is ignorant of Maya and the degrees of reality or of illusion ; it does not conceive of the metaphysical - but not pantheistic - identity between manifestation and the Principle; still less, therefore, does it conceive of the consequence this identity implies from the point of view of the intellect and the knowledge which delivers.(1) The Absolute is not the Absolute inasmuch as it contains aspects, but inasmuch as It transcends them; inasmuch as It is Trinity It is therefore not Absolute.

~ Frithjof Schuon