Religion means to follow the orders of God. The orders of God are what is stated in the scriptures.
A religious person is one who follows the orders of God, thus one who follows the scriptures.
One who does not follow the scriptures is called irreligious. The atheists are at least honest, because they don’t believe in the existence of God and thus His orders cannot be followed. One who claims to be religious but does not follow the scriptures or deviates from them is called a demon, far worse than one who does not believe in God (an atheist).
The Vedic scriptures, compiled by Lord Krishna (God), are a guide for human beings on how to live in this world and achieve liberation after death.
“I am seated in everyone’s heart, and from Me come remembrance, knowledge and forgetfulness. By all the Vedas, I am to be known. Indeed, I am the compiler of Vedānta, and I am the knower of the Vedas.” (Lord Krishna, Bhagavad-Gita 15.15)
The Ramayana states, nigamagama sammatam yad, “If one follows the authoritative evidence of the Vedic scriptures, then all perfection will be received.”
The Vedanta Sutra states, sastra-yonitvat, “One must follow the scriptural evidence in all circumstances.”
“He who discards scriptural injunctions and acts according to his own whims attains neither perfection, nor happiness, nor the supreme destination.” (Lord Krishna, Bhagavad-Gita 16.23)
“But ignorant and faithless persons who doubt the revealed scriptures do not attain God consciousness; they fall down. For the doubting soul there is happiness neither in this world nor in the next.” (Lord Krishna, Bhagavad-Gita 4.40)
“Those persons who execute their duties according to My injunctions and who follow this teaching faithfully, without envy, become free from the bondage of fruitive actions.” (Lord Krishna, Bhagavad-Gita 3.31)
“That action performed in illusion, in disregard of scriptural injunctions, and without concern for future bondage or for violence or distress caused to others is said to be in the mode of ignorance.” (Lord Krishna, Bhagavad-Gita 18.25)
“Those who undergo severe austerities and penances not recommended in the scriptures, performing them out of pride and egoism, who are impelled by lust and attachment, who are foolish and who torture the material elements of the body as well as the Supersoul dwelling within, are to be known as demons.” (Lord Krishna, Bhagavad-Gita 17.5-6)
“Of sacrifices, the sacrifice performed according to the directions of scripture, as a matter of duty, by those who desire no reward, is of the nature of goodness.” (Lord Krishna, Bhagavad-Gita 17.11)
“Any sacrifice performed without regard for the directions of scripture, without distribution of prasādam [spiritual food], without chanting of Vedic hymns and remunerations to the priests, and without faith is considered to be in the mode of ignorance.” (Lord Krishna, Bhagaavd-Gita 17.13)
“That action performed in illusion, in disregard of scriptural injunctions, and without concern for future bondage or for violence or distress caused to others is said to be in the mode of ignorance.” (Lord Krishna, Bhagavad-Gita 18.25)
“Right work is work done in terms of the prescribed directions in the scriptures, and wrong work is work done against the principles of the scriptural injunctions.” (Swami Srila Prabhupada, Bhagavad-Gita 18.15 purport)
“Therefore it is stated here that the demons do not know the scriptural rules, nor do they have any inclination to follow them.” (Swami Srila Prabhupada, Bhagavad-Gita 16.7 purport)