Those who are cultivating spiritual life and executing devotional service are always engaged in activity. Such activity can be performed with the body or with the mind. Thinking, feeling and willing are all activities of the mind, and when we will to do something, the activity comes to be manifest by the gross bodily senses. Thus, in our mental activities we should always try to think of Kṛṣṇa and try to plan how to please Him, following in the footsteps of the great ācāryas and the personal spiritual master. There are activities of the body, activities of the different senses and activities of speech. A Kṛṣṇa conscious person engages his words in preaching the glories of the Lord. This is called kīrtana. And by his mind a Kṛṣṇa conscious person always thinks of the activities of the Lord—as He is speaking on the battlefield of Kurukṣetra or engaging in His various pastimes at Vṛndāvana with His devotees. In this way one can always think of the activities and pastimes of the Lord. This is the mental culture of Kṛṣṇa consciousness.
Similarly, we can offer many services with our bodily activities. But all such activities must be in relationship with Kṛṣṇa. This relationship is established by connecting oneself with the bona fide spiritual master who is the direct representative of Kṛṣṇa in disciplic succession. Therefore, the execution of Kṛṣṇa conscious activities with the body should be directed by the spiritual master and then performed with faith. The connection with the spiritual master is called initiation. From the date of initiation by the spiritual master, the connection between Kṛṣṇa and a person cultivating Kṛṣṇa consciousness is established. Without initiation by a bona fide spiritual master, the actual connection with Kṛṣṇa consciousness is never performed.
This cultivation of Kṛṣṇa consciousness is not material. The Lord has generally three energies—namely, the external energy, the internal energy, and the marginal energy. The living entities are called marginal energy, and the material cosmic manifestation is the action of the external or material energy. Then there is the spiritual world, which is a manifestation of the internal energy. The living entities, who are called marginal energy, perform material activities when acting under the inferior external energy. And when they engage in activities under the internal spiritual energy, their activities are called Kṛṣṇa conscious. This means that those who are great souls or great devotees do not act under the spell of material energy, but act instead under the protection of the spiritual energy. Any activities done in devotional service or in Kṛṣṇa consciousness are directly under the control of spiritual energy. In other words, energy is a sort of strength, and this strength can be spiritualized by the mercy of both the bona fide spiritual master and Kṛṣṇa.
In the Caitanya-caritāmṛta by Kṛṣṇadāsa Kavirāja Gosvāmī, Lord Caitanya states that it is a fortunate person who comes in contact with a bona fide spiritual master by the grace of Kṛṣṇa. One who is serious about spiritual life is given by Kṛṣṇa the intelligence to come in contact with a bona fide spiritual master, and then by the grace of the spiritual master one becomes advanced in Kṛṣṇa consciousness. In this way the whole jurisdiction of Kṛṣṇa consciousness is directly under the spiritual energy—Kṛṣṇa and the spiritual master. This has nothing to do with the material world. When we speak of Kṛṣṇa we refer to the Supreme Personality of Godhead, along with His many expansions. He is expanded by His plenary parts and parcels, His differentiated parts and parcels and His different energies. Kṛṣṇa, in other words, means everything and includes everything. Generally, however, we should understand Kṛṣṇa to mean Kṛṣṇa and His personal expansions. Kṛṣṇa expands Himself as Baladeva, Saṅkarṣaṇa, Vāsudeva, Aniruddha, Pradyumna, Rāma, Nṛsiṁha and Varāha, as well as many other incarnations and innumerable Viṣṇu expansions. These are described in the Śrīmad-Bhāgavatam to be as numerous as the uncountable waves. So Kṛṣṇa includes all such expansions, as well as His pure devotees. In the Brahma-saṁhitā it is stated that Kṛṣṇa's expansions are all complete in eternity, blissfulness and cognizance.