Religion in Latin is=Re (back, again)+Ligare (bind, to unite), i. one which binds one with origin or fountain head that unites you with you.
There is only one religion which is the soul of Christianity or Islam, or Buddhism or Hinduism or whatever it be. It is that by which you gain the ultimate experience- the experience into which merge all distinctions of caste, colour and creed, all doctrines and dogmas, your body, mind and intellect, time, space and causation, this world and all other imaginary worlds. Any systematic attempt, which you undertake to reach that infinite state of being, is religious. The self knows itself by itself.
Knowledge, love and pleasure are transacted through the equipment of the intellect, mind and body. But you never find satiation in them. Religion means going beyond the periphery of the body, mind and intellect and becoming one with Atman, and Brahman, the illimitable Self. The Atman is infinite and all pervading and manifests through the instrumentality of body, mind and intellect like electricity manifests differently in different instrumentality.
Your attention at present is upon the material equipments and their functionings. Consequently you see plurality, diversity everywhere. That vision gives rise to friction and agitation in your life. Whereas, if your attention is focused upon the spiritual core of being, if you learn the art of looking at the Self in all beings you recognise a homogeneity, Unity everywhere. That vision creates harmony, peace and bliss.
Swami Ramatirtha says: "Vedanta brings you a religion which is found in the streets which is written upon the leaves, which is murmured in the brooks, which is whispered in the winds, which is throbbing in your veins and arteries, a religion which concerns your business and bosom, a religion which you have not to practise by going to a particular church, mosque or temple only, a religion which you have to practice and live in your every day life about your hearth, in your dining room, everywhere you will have to live that religion.