Q: Many people say the soul doesn’t have a gender.
In some context, the soul may not have a manifest gender, but inherently it is shakti and therefore essentially feminine by constitution.
A feminine entity can express herself in masculine ways, or visa versa, so the soul can sometimes exhibit a male form without changing the fact that fundamentally it is a female thing.
Q: Krishna says he is param purush (supreme male). But at the same time soul is not prakriti (material energy / female), it’s marginal energy.
All energy of the purusha is prakriti. But we can subdivide it into three categories: para-, apara-, and parāpara–prakriti. The spiritual reality is manifest through para-prakriti, the material reality through apara-prakriti, and the conscious entities (“souls”) through parāpara-prakṛti. Therefore the soul is prakṛti, specifically it is “marginal” prakṛti, or parāpara-prakṛti.
The term prakriti is synonymous with śakti (energy). pra-krti means “the fountainhead of doing.” It is the power that enables a cause to produce effects.
Purusha (śaktimān) establishes the essential nature of masculinity. Prakriti (śakti) establishes the essential nature of masculinity.
It is a little misleading to say, “prakṛti is feminine,” because it sounds like we are ascribing femininity to it. Quite the opposite is true. The female gender is the ascription, due to its similarity to the nature of śakti / prakṛti. In other words, female gender is denoted as “female” because it bears some essential trait in common with the essential trait of the actual female entity, śakti. As mentioned before, the essential trait of śakti / prakṛti is that “it is the power enabling a cause to produce effects.” Prakṛti enables the puruṣa to expand. So, another synonym of prakriti is strī (a word used to denote the female gender, which literally means, “that which grants expansion.”) This facility for expansion is the essence of femininity, which the “female” gender emulates beginning with but not limited to its biological role in reproduction.
All of existence besides the original cause, Bhagavān, is a product of either para-, apara-, or parāpara-prakṛti. Therefore everything in creation is fundamentally feminine. This simply means that everything has the fundamental nature of facilitating the expansion of bliss of the Original Person.
The female biology does not have a monopoly on this essential trait. Any biological gender can act as śakti. For example, the boys of Vṛndāvana expand and facilitate Krishna’s desire to make his bliss more elaborate and fulfilling by enhancing the value and rarity of the time he spends directly with the original female manifestations of śakti, the girls of Vṛndāvana. All quantums of prakṛti expand the bliss of the Original Being, but some do it through masculine forms, others through feminine forms, and still others in neuter forms. Thus all are fundamentally feminine, but can express that femininity through masculine, feminine or neuter vehicles, depending upon the specifics of the role they like to play in the līlā of Bhagavān’s ānanda.
Q: When souls go back to godhead, do they get spiritual bodies with a gender according to their natural Rasa?
Yes, they get forms that facilitate their cherished desires. It is the same principle that operates in the material reflection of reality. A soul develops and exhibits a bodily form that matches and facilitates its cherished desires (in the material reflection, we have the inescapable caveat “as far as possible”). So, in the spiritual realm, we exhibit a form / “body” that facilitates our specific treasured desires to please Krishna.
Q: The souls in madhurya rasa [romantic relationship to the divine], do they always get female form like that of the gopis?
As far as those souls directly and explicitly in Mādhurya Rasa, yes. There could potentially be some exception: perhaps in the case of mohinī-mūrti — a feminine direct manifestation of Bhagavān, but mohini-mūrti is an aiśvarya-avatāra who is not open to forming very intimate, egalitarian relationships with souls so that is ruled out. Sometimes the gopīs jest that a flute is masculine (by grammatical gender), yet Krishna always kisses it. However, most of the time, they describe the flute as feminine. And objectively speaking, it is neuter. So really, there is no literal exception to the principle that all souls directly in mādhurya-rāsa exhibit feminine forms. The flute might be seen as an example of a neuter entity directly in Mādhurya Rāsa, but because the flute does not exhibit a form that expresses sentience (although possessing sentience), it is directly in śānta-rāsa, and that śānta-rasa is engaged as a tool for mādhurya-rāsa. So the flutes mādhurya-rasa is indirect.
In indirect mādhurya-rasa, any of the three genders (male, female, neuter) can participate. In this sense, every resident of Vṛndāvana is in Mādhurya Rasa. All of Vṛndāvana is focused on the parakiya mādhurya rasa of Rādhā-Krishna. Even Krishna’s male friends are focused only on augmenting the excitement of Rādhā-Krishna’s romantic līlā. Even Krishna’s mother and father do what they do only to play a key role in facilitating the sweetness of Krishna’s mādhurya-līlā with Rādhārāṇī. Therefore although in a sense they are in sakhya or vatsalya rasa, actually that sakhya or vataslya is a tool to serve the fundamental mādhurya rasa shared by every molecule and atom of Vṛndāvana Dhāma.
Everyone and everything, trees, flute, peacocks, peacock feathers, monkeys, vines, pathways, sun and moon, boys and girls, men and women, hills and valleys, rivers and pools… everyone and everything in Vṛndāvana is immersed in Rādhā-Krishna’s mādhurya-līlā.