Serving Krsna the Supreme Personality of Godhead and cause of all causes, is accomplished by the marginal living entities (jiva-souls) by ONLY having "free will."

Free will gives the jiva-souls the ability to express themselves in their own unique way to voluntarily make their own choices in their exchanges with Krsna in the spiritual world.

Free will must always exist in the spiritual world because if the individual jiva-souls are forced to love Krsna and only do everything His way, then how can there be genuine loving exchanges and personal contributions in one's relationship with Krsna?

Loving relationships are always a "two-way" street based on reciprocation and loving exchanges, it is never a slave domineering master relationship that only destroys one's ability of self expression (free will) and a sense of individual existence.

Voluntary remaining on the Vaikuntha planets or Goloka-Vrindavana in the spiritual world eternally, is based on the marginal living entities (jiva-souls) responsible execution of their free will

Being able to voluntarily choose to engage in loving exchanges in different ways while serving Krsna, is how devotional service really works in the spiritual world.

Srila Prabhupada - "Love is reciprocal, voluntary, good exchange of feeling, then there is love. Not by force! Krsna does not want to become a lover like that, ‘You love me, otherwise I shall kill you!" (Washington DC July 8, 1976)

Srila Prabhupāda – "Love means a relationship between "two persons," then there is exchange, then there is love. I must deal with you open-hearted, you must deal with me open-hearted, then there is love. So if you want to love Kṛṣṇa, God, then these things must be there." (Aug 9, 1976, Tehran)

Srila Prabhupada - "Love means you take and you give also. Suppose if you love somebody and you simply take from him, but you don't give. Oh, do you think it is very good? No. It is not good. That is NOT love. That is exploitation. If I go on simply taking from you, and if I don't offer you anything, that is simply exploitation." (Lecture BG, Ch 9 text 2-5, New York City, Nov 23, 1966)

Srila Prabhupada - "We have got the propensity to love. Love means somebody else. Love cannot be one or love cannot be executed by only one, personally. There must be another one. I love somebody; somebody loves me, there must be lover, there must be beloved, and the transaction, then love." (SB, Canto 1 Ch 2 text 6, Delhi, Nov 12, 1973)

Srila Prabhupada - "The impersonalist philosophy is oneness, so how there be love with just one? Is it possible? Have you got any such experience that love means one? No. Love means two. There MUST be two, the lover and the beloved. Kṛṣṇa is already lover. He loves you so much that He's trying to get you back. That is Kṛṣṇa's attempt. "Please, My dear boy, or My dear friend, My dear servant." (SB, Canto 2 Ch 1 text 3, Paris, June 12, 1974)

On the Vaikuntha planets and Goloka-Vrindavana, no two jiva-souls are the same, each has their own unique individual personality, character and spiritual bodily form eternally.

Even with such selfless emotions of loving devotion and dedication, the jiva-souls NEVER lose their free will, individuality identity and unique personality.

Each individual jiva-soul (marginal living entity) is part and parcel of Kṛṣṇa the Supreme Personality of Godhead and cause of all causes.

However, all jiva-souls have a separated existence from Krsna that He allows them to experience diversity, mystery and intrique.  

The perpetual make up or constitution of the marginal living entities (jiva-souls) is they always have the freedom in the spiritual world to voluntarily serve Krsna in so many ways, or reject Him.

In this way, each jiva-soul has their own individual sense of self, unique character, personality and spiritual bodily features in the spiritual world based on how they want to voluntarily serve Krsna or Visnu.

Srila Prabhupada - "The jiva-soul's position in the spiritual world is voluntary, some devotees want to serve Krsna as a flower; they become flower there. If I want to be a flower I shall lie down at the lotus feet of Krsna and become flower, voluntarily, and he can change from flower to human body, that is spiritual life. There is no restriction. If some devotee wants to serve Krsna as cow, he serves Krsna as cow, as calf, as flower, as plant, as water, as ground, field, or as father, as mother, as friend, as beloved, anything. It is inconceivable, yet a fact." (SB, Canto 6 Ch 1 Text 1-4, Melb, Australia May 20, 1975)

In the spiritual world ALL relationships with Krsna are "equally blissful to each other", just like one may like a carnation flower while others may choose to like a rose flower.

The marginal living entities (jiva-souls) can NEVER lose their free will in the spiritual world which allows them to always voluntary choose how to serve Visnu on the Vaikuntha planets, or Kṛṣṇa on Goloka Vrindavana. 

Srila Prabhupada - "If you have no free will, then you are a stone. The stone has no free will. You want to be stone? Then you must have free will! But don't misuse your free will. But don't try to become stone either. That is not life." (Aug 5, 1976, New Mayapur France)

In the Vaikuntha planets and Goloka Vrindavana, the individual jiva-souls are never denied their independent nature of voluntary service. The jiva-souls never attempt to extinguish their individual identity, independent contributions, free will and unique character and personality, thinking by giving these up is the real meaning of surrendering to Krsna. No, actually this loveless idea of surrender is impersonalism and spiritual suicide.

Being the unique individual PERSON the jiva-souls eternally are, they always have their free will in the spiritual world. This allows them to voluntarily serve Krsna the way the choose, or reject His assocition also.

Srila Prabhupada - "So, unless there is a possibility of misusing our free will, there is no question of freedom." (Dialectical Spiritualism) 

The individual jiva-souls in the spiritual world always voluntarily express themselves in their own unique way with personal contributions they offer to Krsna.

Srila Prabhupada - "Because you are Son of God you have independence, you have acquired the quality of your father, so God does not interfere with your independence. If you persist that “I must enjoy independently,” God says, “All right, you can go.” This is the position, if you persist, God sanctions. And you can come here and enjoy." (Melb, Australia June 25, 1974)

Srila Prabhupada – "So everyone can know that independence means one can use it properly, or one can misuse it. That is independence. If you make it one way only, that is not independence, that is force." (Los Angeles, June 23, 1975)

Srila Prabhupada – "You are part and parcel of God and have your independence, if he likes, he can return, that independence has to be accepted, we can misuse that. Such misuse is the cause of our falldown." (Conversation, Mayapur, Feb 19, 1976)

Srila Prabhupada - "Free will means that you can act wrongly, that is free will. Unless there is chance of doing wrong or right, there is no question of free will." Where is "free will" then? If I act only one sided, that means I have no "free will." Because we act sometimes wrongly, that means free will."

Hayagriva Dasa - "A man may know better but still act wrongly."

Srila Prabhupada - "Yes, but that is free will, he misuses his. Just like a thief, he knows that his stealing, it is bad, but still he does it. That is free will. He cannot check his greediness, so in spite of his knowing that he is doing wrong thing—he will be punished, he knows; he has seen another thief, he was punished, he was put into prison— everything he knows, but still he steals. Why? Misuse of free will. Unless there is misuse of free will, there is no question of free will." (Excerpt from: Philosophy Discussions on Rene Descartes)

This infinitly (eternal) existing makeup of each individual jiva-soul has no beginning or end, and is part and parcel and the eternal constitution of every marginal living entity (jiva-soul) as Bhagavad Gita As It Is teaches.

This means the individual jiva-souls are always aware of their own personality and independent nature that is separate from Krsna's Personality.