Antaḥ kṛṣṇa refers to one who is always thinking of Kṛṣṇa. This attitude is a predominant feature of Śrīmatī Rādhārāṇī. Even though many devotees always think of Kṛṣṇa, none can surpass the gopīs, among whom Rādhārāṇī is the leader in thinking of Kṛṣṇa. Rādhārāṇī’s Kṛṣṇa consciousness surpasses that of all other devotees. Lord Caitanya accepted the position of Śrīmatī Rādhārāṇī to understand Kṛṣṇa; therefore He was always thinking of Kṛṣṇa in the same way as Rādhārāṇī. By thinking of Lord Kṛṣṇa, He always overlapped Kṛṣṇa.
(Sri Caitanya Caritamrta----1:3:81----translation).

In this chapter of the epic Caitanya-caritāmṛta, Kṛṣṇadāsa Kavirāja Gosvāmī has stressed that Lord Caitanya appeared for three principal purposes of His own. The first purpose was to relish the position of Śrīmatī Rādhārāṇī, who is the prime reciprocator of transcendental love of Śrī Kṛṣṇa. Lord Kṛṣṇa is the reservoir of transcendental loving transactions with Śrīmatī Rādhārāṇī. The subject of those loving transactions is the Lord Himself, and Rādhārāṇī is the object. Thus the subject, the Lord, wanted to relish the loving mellow in the position of the object,Rādhārāṇī.
The second reason for His appearance was to understand the transcendental mellow of Himself. Lord Kṛṣṇa is all sweetness. Rādhārāṇī’s attraction for Kṛṣṇa is sublime, and to experience that attraction and understand the transcendental sweetness of Himself, He accepted the mentality of Rādhārāṇī.
The third reason that Lord Caitanya appeared was to enjoy the bliss tasted by Rādhārāṇī. The Lord thought that undoubtedly Rādhārāṇī enjoyed His company and He enjoyed the company of Rādhārāṇī, but the exchange of transcendental mellow between the spiritual couple was more pleasing to Śrīmatī Rādhārāṇī than to Śrī Kṛṣṇa. Rādhārāṇī felt more transcendental pleasure in the company of Kṛṣṇa than He could understand without taking Her position, but for Śrī Kṛṣṇa to enjoy in the position of Śrīmatī Rādhārāṇī was impossible because that position was completely foreign to Him. Kṛṣṇa is the transcendental male, and Rādhārāṇī is the transcendental female. Therefore, to know the transcendental pleasure of loving Kṛṣṇa, Lord Kṛṣṇa Himself appeared as Lord Caitanya, accepting the emotions and bodily luster of Śrīmatī Rādhārāṇī.
(Sri Caitanya Caritamrta----1:4---summary).

This imperative is applicable to pure devotees. Neophytes will be able to understand these affairs only after being elevated by regulated devotional service under the expert guidance of the spiritual master. Then they too will be competent to hear of the love affairs of Rādhā and Kṛṣṇa.
As long as one is in material, conditioned life, strict discipline is required in the matter of moral and immoral activities. The absolute world is transcendental and free from such distinctions because there inebriety is not possible. But in this material world a sexual appetite necessitates distinction between moral and immoral conduct. There are no sexual activities in the spiritual world. The transactions between lover and beloved in the spiritual world are pure transcendental love and unadulterated bliss.
One who has not been attracted by the transcendental beauty of rasa will certainly be dragged down into material attraction, thus to act in material contamination and progress to the darkest region of hellish life. But by understanding the conjugal love of Rādhā and Kṛṣṇa one is freed from the grip of attraction to material so-called love between man and woman.
(Sri Caitanya Caritamrta----1:4:35----purport).

Svarūpa Dāmodara Gosvāmī has described Lord Caitanya as Kṛṣṇa Himself with the attitude of Rādhārāṇī, or a combination of Rādhā and Kṛṣṇa. The intention of Lord Caitanya is to taste Kṛṣṇa's sweetness in transcendental love. He does not care to think of Himself as Kṛṣṇa, because He wants the position of Rādhārāṇī. We should remember this. A class of so-called devotees called the nadīyā-nāgarīs or gaura-nāgarīs pretend that they have the sentiment of gopīs toward Lord Caitanya, but they do not realize that He placed Himself not as the enjoyer, Kṛṣṇa, but as the enjoyed, the devotee of Kṛṣṇa. The concoctions of unauthorized persons pretending to be bona fide have not been accepted by Lord Caitanya. Presentations such as those of the gaura-nāgarīs are only disturbances to the sincere execution of the mission of Lord Caitanya. Lord Caitanya is undoubtedly Kṛṣṇa Himself, and He is always nondifferent from ŚrīmatīRādhārāṇī. But the emotion technically called vipralambha-bhāva, which the Lord adopted for confidential reasons, should not be disturbed in the name of service. A mundaner should not unnecessarily intrude into affairs of transcendence and thereby displease the Lord. One must always be on guard against this sort of devotional anomaly. A devotee is not meant to create disturbances to Kṛṣṇa. As Śrīla Rūpa Gosvāmī has explained, devotional service is ānukūlyena, or favorable to Kṛṣṇa. Acting unfavorably toward Kṛṣṇa is not devotion. Kaṁsa was the enemy of Kṛṣṇa. He always thought of Kṛṣṇa, but he thought of Him as an enemy. One should always avoid such unfavorable so-called service.
Lord Caitanya has accepted the role of Rādhārāṇī, and we should support that position, as Svarūpa Dāmodara did in the Gambhīrā (the room where Lord Caitanya Mahāprabhu stayed in Purī). He always reminded Lord Caitanya of Rādhā’s feelings of separation as they are described in Śrīmad-Bhāgavatam, and Lord Caitanya appreciated his assistance. But the gaura-nāgarīs, who place Lord Caitanya in the position of enjoyer and themselves as His enjoyed, are not approved by Lord Caitanya or by Lord Caitanya's followers. Instead of being blessed, the foolish imitators are left completely apart. Their concoctions are against the principles of Lord Śrī Caitanya Mahāprabhu. The doctrine of transcendental enjoyment by Kṛṣṇa cannot be mixed up with the doctrine of transcendental feeling of separation from Kṛṣṇa in the role of Rādhārāṇī.
(Sri Caitanya Caritamrta----1:4:41----purport).

The transcendental mellow relished by the gopīs in Vraja is superexcellently featured in Śrīmatī Rādhārāṇī. Mature assimilation of the transcendental humor of conjugal love is represented by Śrīmatī Rādhārāṇī, whose feelings are incomprehensible even to the Lord Himself. The intensity of Her loving service is the highest form of ecstasy. No one can surpass Śrīmatī Rādhārāṇī in relishing the qualities of the Lord through this supreme transcendental mellow. Therefore the Lord Himself agreed to assume the position of Rādhārāṇī in the form of Lord Śrī Gaurāṅga. He then relished the highest position of parakīya-rasa, as exhibited in the transcendental abode of Vraja.
(Sri Caitanya Caritamrta----1:4:50----purport).

“The loving affairs of Śrī Rādhā and Kṛṣṇa are transcendental manifestations of the Lord's internal pleasure-giving potency. Although Rādhāand Kṛṣṇa are one in Their identity, They separated Themselves eternally. Now these two transcendental identities have again united, in the form of Śrī Kṛṣṇa Caitanya. I bow down to Him, who has manifested Himself with the sentiment and complexion of Śrīmatī Rādhārāṇī although He is Kṛṣṇa Himself.”
(Sri Caitanya Caritamrta----1:4:55----translation).

Rādhā and Kṛṣṇa are one and the same, but They have assumed two bodies. Thus They enjoy each other, tasting the mellows of love.
The two transcendentalists Rādhā and Kṛṣṇa are a puzzle to materialists. The above description of Rādhā and Kṛṣṇa from the diary of Śrīla Svarūpa Dāmodara Gosvāmī is a condensed explanation, but one needs great spiritual insight to understand the mystery of these two personalities. One is enjoying in two. Śrī Kṛṣṇa is the potent factor, and Śrīmatī Rādhārāṇī is the internal potency. According to Vedānta philosophy, there is no difference between the potent and the potency; they are identical. We cannot differentiate between one and the other, any more than we can separate fire from heat.
Everything in the Absolute is inconceivable in relative existence. Therefore in relative cognizance it is very difficult to assimilate this truth of the oneness between the potent and the potency. The philosophy of inconceivable oneness and difference propounded by Lord Caitanya is the only source of understanding for such intricacies of transcendence.
In fact, Rādhārāṇī is the internal potency of Śrī Kṛṣṇa, and She eternally intensifies the pleasure of Śrī Kṛṣṇa. Impersonalists cannot understand this without the help of a mahā-bhāgavata devotee. The very name "Rādhā" suggests that Śrīmatī Rādhārāṇī is eternally the topmost mistress of the comforts of Śrī Kṛṣṇa. As such, She is the medium transmitting the living entities' service to Śrī Kṛṣṇa. Devotees in Vṛndāvana therefore seek the mercy of Śrīmatī Rādhārāṇī in order to be recognized as loving servitors of Śrī Kṛṣṇa.
(Sri Caitanya Caritamrta----1:4:55----translation and purport).

Śrīmatī Rādhikā is the transformation of Kṛṣṇa's love. She is His internal energy called hlādinī.
(Sri Caitanya Caritamrta----1:4:59---- purport).

Śrī Rādhā Ṭhākurāṇī is the embodiment of mahābhāva. She is the repository of all good qualities and the crest jewel among all the lovely consorts of Lord Kṛṣṇa.
The unadulterated action of the hlādinī-śakti is displayed in the dealings of the damsels of Vraja and Śrīmatī Rādhārāṇī, who is the topmost participant in that transcendental group. The essence of the hlādinī-śakti is love of Godhead, the essence of love of Godhead is bhāva, or transcendental sentiment, and the highest pitch of that bhāva is called mahābhāva. ŚrīmatīRādhārāṇī is the personified embodiment of these three aspects of transcendental consciousness. She is therefore the highest principle in love of Godhead and is the supreme lovable object of Śrī Kṛṣṇa.
(Sri Caitanya Caritamrta----1:4:69----translation and purport).