A similar statement is there in the Eleventh Canto of Śrīmad-Bhāgavatam, 2nd Chapter, 5th verse, where Havi, the son of King Ṛṣabha, addresses Mahārāj Nimi: "My dear King, a person who never deviates even for a moment from engagement in service at the lotus feet of the Supreme Person (engagement which is sought after even by great demigods like Indra) with firm conviction that there is nothing more worshipable or desirable than this, is called the first-class devotee."
Śrī Rūpa Gosvāmī says that a neophyte devotee who has simply developed a slight love of Godhead is certainly a prospective candidate for devotional service. When he becomes firmly fixed in such devotional service, that assured status becomes a confidential part of his devotional service.
Sometimes it is found that a pure devotee lies down in the temple of the Lord in order to serve Him as a confidential friend. Such friendly behavior of a devotee may be accepted as rāgānugā, or spontaneous. Although, according to regulative principles, no one can lie down in the temple of the Supreme Personality of Godhead, this spontaneous love of Godhead can be grouped under devotional service in friendship.
Regarding complete self-surrender, there is a nice description in the Eleventh Canto of Śrīmad-Bhāgavatam, 29th Chapter, 32nd verse, where the Lord says: "A person who has completely surrendered unto Me and has completely given up all other activities is protected by Me personally, both in this life and in the next. In other words, I wish to help him become more and more advanced in spiritual life. Such a person is to be understood as having already achieved sārṣṭi (having equal opulences with the supreme)." It is also confirmed in the Bhagavad-gītā that as soon as a person surrenders unto the lotus feet of Kṛṣṇa, Kṛṣṇa takes charge of him and gives him a guarantee of protection from all sinful reactions. He also instructs from within, so that the devotee may very quickly make advancement towards spiritual perfection.
This self-surrender is called ātma-nivedana. According to different authorities, "self" is differently defined. "Self" is sometimes considered to refer to the spirit self, or soul, and "self" is sometimes considered to refer to the mind or to the body. Full self-surrender, therefore, means not only surrendering one's self as spirit soul, but also surrendering one's mind and body to the service of the Lord. Śrīla Bhaktivinode Thākur has sung a nice song in this connection. While offering himself as a fully surrendered soul, he said, "My mind, my household affairs, my body, whatever is in my possession, my dear Lord, I offer to You for Your service. Now You can do with them as You like. You are the supreme possessor of everything, so if You like You can kill me, or if You like You can give me protection. All authority belongs to You. I have nothing to claim as my own."
Śrī Yāmunācārya, in his prayers to the Lord, has expressed a similar idea in the following words: "My dear Lord, I may be living within some body as a human being or as a demigod, but whatever mode of life, I do not mind, because these bodies are simply by-products of the three modes of material nature, and I, who am in possession of these bodies, am surrendering myself unto You."