"In the process of worshiping the Deity it is sometimes enjoined that one worship the Deity within the mind. In the Padma Purāna, Uttara-khanda, it is said, "All persons can generally worship within the mind." ...In the Nārada-pañcarātra it is stated by Lord Nārāyana that worship of the Deity within the mind is called mānasa-pūjā. One can become free from the four miseries by this method."
(Śrīla Prabhupāda - Śrīmad Bhāgavatam 7.5.23-24)
This is actually a standard practice in Iskcon, outlined in the Pancaratra-Pradipa Manual: "After meditating on the form of the Lord, you should engage your mind in worshiping that form. Dhyana is the preparation for manasa-puja; whereas dhyana is passive, manasa-puja is active. Whatever items you offer externally you should first offer internally with full devotion and attention. Also, whereas the items offered in external worship may be simple due to modest means, in the course of manasa-puja one may perform very opulent worship of the Lord."
Moreover, this section states: "The sastra points out that for one performing sadhana-bhakti, the puja with paraphernalia is ineffective without manasa-puja. Puja performed with paraphernalia but without manasa-puja may be the cause of offense for the neophyte, for he will tend to see the Deity as a material object. Thus manasa-puja, or antar-yoga, is essential in all types of Deity worship.
...
Both dhyana and manasa-puja are performed not only for the main Deity, but also for the spiritual master and Lord Caitanya in preliminary worship."
Physical worship of Deity and the chanting of the Maha Mantra Hare Krsna must be accompanied by meditation (dhyana) and mental service (manasa puja or manasi seva).
Meditate on the form of the Guru, meditate in the form of Gauranga, meditate in the form of Radha Krsna, meditate on Navadvipa, meditate on Vrndavana and then later make Manasi Seva (mental service). Only after then do external worship.
Only in this way will the physical worship be validated.
This is called ANTARA YOGA. Antara means in the heart.
ANTARA YOGA = yoga practice with the heart.
Prabhupada explains how to do manasi seva related with the Maha Mantra:
"The Hare Krishna mantra chanting means keeping Krishna always within your heart. It is not expensive at all. You haven't got to make a very exalted throne for Krishna. You can imagine that "In my heart I have placed a diamond throne, and Krishna is sitting." That is accepted and actually it becomes. Even within the mind, you think that "I have kept one diamond throne, very costly throne. Because Krishna is coming, He will sit down here." That is not false; that is fact.
"So you create such a situation in your heart, "Now Krishna has seated. Let me wash His feet with Ganges water or Yamuna water. Now I change His dress to first-class costly garments. then I decorate Krishna with ornaments. Then I give Him something for eating." You can simply think of this. This is meditation. It is such a nice thing. Anywhere you can sit down, and think that Krishna is sitting in your heart and you are receiving Him in such a nice way. This is not false; this fact; this is easy." (Srila Prabhupada talk (1/6/74))
