Sincerity...

It does not matter in what way a person offers his respect and his reverence to the deity he worships; it matters only how sincere he is in his offering.

Bowl of Saki, by Hazrat Inayat Khan
Commentary by Pir-o-Murshid Inayat Khan:

The forms of worship of all the different religions are necessarily different. It depends upon what one is accustomed to, what is akin to one's nature. One cannot make a common rule and say that this form is wrong and that form is right. One person will perhaps feel more exaltation in a form of worship which includes some art. It stimulates his emotional nature. Music, pictures, perfumes, colors, and light, all these have an effect upon such a person. Another can concentrate better if there is nothing in the place of worship to catch his attention. It is all a matter of temperament. It is not wrong to prefer the one or the other. The Sufi sees the variety of forms as different ideals. He does not attach importance to the outer expression. If there is a sincere spirit behind it, if a person has a feeling for worship, it does not matter what form of worship it is.

In what manner prayer be offered matters little if only the sentiment be right. The orthodox world has fought with each other, each claiming that, "Our manner of prayer is the best. Our church is the best. Our temple is the best. Our sermon is the best. The others are astray;" not knowing that in the house of God it is not asked, "To which church do you belong? To which temple do you belong?" but it is asked, "How sincere were you in your prayer?"

Nature teaches every soul to worship God in some way or other, and often provides that which is suitable for each. Those who want one law to govern all have lost sight of the spirit of their own religion. And it is in people who have not yet learned their own religion that such ideas are commonly found. Did they but know their own religion, how tolerant they would become, and how free from any grudge against the religion of others!

So it is too with the manner of worship. It does not matter in what way a person offers his respect and his reverence to the deity he worships. It only matters how sincere he is in his offering. In one house of God we find that people do not wear hats; in Hindustan, Persia, and Arabia they put on turbans to go to the mosque. That is their custom. It makes no difference whether one person prays standing, another sitting, another kneeling, another prostrating himself, another in company with other people and another alone. All that matters is that the heart of the worshipper is pure, that the mind is connected with God, that there is sincerity and earnestness.