In conditioned life the consciousness in the body is the cause of bondage, but the same consciousness, when transformed into Kṛṣṇa consciousness, becomes the cause for one's returning home, back to Godhead. The human body, therefore, may be used in two ways—for going to the darkest regions of ignorance or for going forward, back home, back to Godhead. To go back to Godhead, the path is mahat-sevā, to accept the self-realized spiritual master. Mahat-sevāṁ dvāram āhur vimukteḥ [SB 5.5.2]. For liberation, one should accept the direction of authorized devotees who can actually endow one with perfect knowledge.
(Srimad Bhagavatam---7:15:41---purport).

Sometimes a neophyte devotee offers all the paraphernalia for worshiping the Lord, and he factually worships the Lord as the Deity, but because he is envious of the authorized devotees of Lord Viṣṇu, the Lord is never satisfied with his devotional service.
Deity worship is especially meant for purifying the neophyte devotees. Actually, however, preaching is more important. In Bhagavad-gītā (18.69) it is said, na ca tasmān manuṣyeṣu kaścin me priya-kṛttamaḥ: if one wants to be recognized by the Supreme Personality of Godhead, he must preach the glories of the Lord. One who worships the Deity must therefore be extremely respectful to preachers; otherwise simply worshiping the Deity will keep one in the lower stage of devotion.
(Srimad Bhagavatam----7:14:41----translation and purport).

The demigods are expanded parts and parcels of the Supreme Lord Viṣṇu, and they are embodied by time, external energy and partial consciousness of the Supreme. Human beings, animals, birds, etc., are also parts and parcels of the Lord and have different material bodies, but they are not the controlling deities of material affairs. They are, rather, controlled by such demigods. Such control is not superfluous; it is as necessary as the controlling departments in the affairs of a modern state. The demigods should not be despised by the controlled living beings. They are all great devotees of the Lord entrusted to execute certain functions of universal affairs. One may be angry with Yamarāja for his thankless task of punishing sinful souls, but Yamarāja is one of the authorized devotees of the Lord, and so are all the other demigods. A devotee of the Lord is never controlled by such deputed demigods, who function as assistants of the Lord, but he shows them all respects on account of the responsible positions to which they have been appointed by the Lord.
(Srimad Bhagavatam----3:5:38---purport).

One cannot offer prayers to the Lord with mundane words. One must become spiritually advanced by controlling the mind and senses. Then he can find suitable words to offer in prayers to the Lord. Quoting the following verse from the Padma Purāṇa, Śrīla Sanātana Gosvāmī forbids us to sing any song not sung by authorized devotees.
avaiṣṇava-mukhodgīrṇaṁ
pūtaṁ hari-kathāmṛtam
śravaṇaṁ naiva kartavyaṁ
sarpocchiṣṭaṁ yathā payaḥ
The words or songs of a person not fixed in Vaiṣṇava behavior, not strictly following the rules and regulations and chanting the Hare Kṛṣṇa mantra should not be accepted by pure devotees.
(Srimad Bhagavatam---6:16:33---purport).

"A person who is very faithfully engaged in the worship of the Deity in the temple but does not know how to behave toward devotees or people in general is called a prākṛta-bhakta, or kaniṣṭha-adhikārī." A prākṛta devotee, or neophyte devotee, is still on the material platform. He certainly engages in worshiping the Deity, but he cannot appreciate the activities of a pure devotee. It has actually been seen that even an authorized devotee who is engaged in the service of the Lord by preaching the mission of Kṛṣṇa consciousness is sometimes criticized by neophyte devotees. Such neophytes are described by Viśvanātha Cakravartī Ṭhākura: sarva-prāṇi-sammānanāsamarthānām avajñā spardhādimatāṁ tu bhagavat-pratimaiva pātram ity āha. For those who cannot properly appreciate the activities of authorized devotees, Deity worship is the only way for spiritual advancement. In the Caitanya-caritāmṛta (Antya 7.11) it is clearly said, kṛṣṇa-śakti vinā nahe tāra pravartana: without being authorized by Kṛṣṇa, one cannot preach the holy name of the Lord throughout the entire world. Nevertheless, a devotee who does so is criticized by neophyte devotees, kaniṣṭha-adhikārīs, who are on the lower stages of devotional service. For them, Deity worship is strongly recommended.
(Srimad Bhagavatam----7:14:30---purport).