Other rules are that one should not offer foodstuff which is cooked by a non-Vaiṣṇava. One should not worship the Deity before a nondevotee. One should not engage himself in the worship of the Lord while seeing a nondevotee. One should begin the worship of the demigod Gaṇapati, who drives away all impediments in the execution of devotional service. In the Brahma-saṁhitā it is stated that Gaṇapati worships the lotus feet of Lord Nṛsiṁhadeva, and in that way he has become auspicious for the devotees in clearing out all impediments. Therefore, all devotees should worship Gaṇapati. The Deities should not be bathed in water which has been touched by the nails or fingers. When a devotee is perspiring, he should not engage himself in worshiping the Deity. Similarly, there are many other prohibitions, such as one should not cross or step over the flowers offered to the Deities, nor should one take a vow in the name of God. These are all different kinds of offenses in the matter of executing devotional service, and one should be careful to avoid them.
In the Padma Purāṇa it is stated that even a person whose life is completely sinful will be completely protected by the Lord if he simply surrenders unto Him. So it is accepted that one who surrenders unto the Supreme Personality of Godhead becomes freed from all sinful reactions.
And even when a person becomes an offender unto the Supreme Personality of Godhead Himself, he can still be delivered simply by taking shelter of the holy names of the Lord: Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. In other words, the chanting of Hare Kṛṣṇa is beneficial for eradicating all sins; but if one becomes an offender to the holy names of the Lord, then he has no chance of being delivered.
The offenses against the chanting of the holy name are as follows: 1) To blaspheme the devotees who have dedicated their lives for propagating the holy name of the Lord. 2) To consider the names of demigods like Lord Śiva or Lord Brahmā to be equal to, or independent of, the name of Lord Viṣṇu. (Sometimes the atheistic class of men take it that any demigod is as good as the Supreme Personality of Godhead, Viṣṇu. But one who is a devotee knows that no demigod, however great he may be, is independently as good as the Supreme Personality of Godhead. Therefore if someone thinks that he can chant Kālī, Kālī! or Durgā, Durgā! and it is the same as Hare Kṛṣṇa, that is the greatest offense.) 3) To disobey the orders of the spiritual master. 4) To blaspheme the Vedic literature or literature in pursuance of the Vedic version. 5) To consider the glories of chanting Hare Kṛṣṇa as imagination. 6) To give some interpretation on the holy name of the Lord. 7) To commit sinful activities on the strength of the holy name of the Lord. (Because by chanting the holy name of the Lord one can be freed from all kinds of sinful reactions, it should not be taken that one may continue to act sinfully and after that chant Hare Kṛṣṇa to neutralize his sins. Such a dangerous mentality is very offensive and should be avoided.) 8) To consider the chanting of Hare Kṛṣṇa as one of the auspicious ritualistic activities which are offered in the Vedas as fruitive activities (karma-kāṇḍa). 9) To instruct a faithless person about the glories of the holy name. (Anyone can take part in chanting the holy name of the Lord, but in the beginning one should not be instructed about the transcendental potency of the Lord. Those who are too sinful cannot appreciate the transcendental glories of the Lord, and therefore it is better not to instruct them in this matter.) 10) To not have complete faith in the chanting of the holy names and to maintain material attachments, even after understanding so many instructions on this matter.
Every devotee who claims to be a Vaiṣṇava must guard against these offenses in order to quickly achieve the desired success.