In reality, the jiva, now known after salvation as pure personality (purusa), continues to maintain its separate existence, but as a devotee of God. The purusa is eternally a servant of God; it does not become God. Indeed, such an idea would be anathema to the bhaktic circle of the Bhagavata Purana—a text which is regarded by Sankaradeva and Madhavadeva as the very essence of Vedanta.
Instead, by the jiva (or purusa) merging into Isvara, what is really meant is this: the pure personality which had, due to envelopment by the ignorance (avidya) of primal matter (maya), fallen into a matter-like existence, by taking sole-refuge (eka sarana) in the Lord and doing pure devotion (bhakti) to Him, becomes purified (suddha), and, on death, returns finally to the spiritual abode of the Lord. He returns to God, as it were. Otherwise, after death, the unenlightened pure personality would return once again to matter. This only is the eschatological implication.
There is a conceptual model associated with the process of material evolution outlined in the theistic samkhya of the Bhagavata, which one must be acquainted with, in order to make sense of what is being said here. In this conceptual model, the effect (karya) resides in the cause (karana). The entire creation evolves as a result of an initial actuation of a primal material substance known as prakrti (also anthropomorphized in the Puranic world as ‘Laksmi’) by the Lord. All the evolutes of the material creation emanate from prakrti. This is a very exciting process.
To explain it in simple terms, there is a causal chain, with one evolute being the effect (karya) of the evolute (‘evolutand’) immediately preceding it which is its cause (karana). The evolutes reside within the evolutands; by the action of an agent such as time, they (the evolutes) emerge from their causes. This is material evolution (parinama), pure and simple. And the pure personalities (purusas), though they themselves are immutable (avikari) and not subject to evolution, find themselves embedded into the creation—both the macrocosm as well as the microcosm.
Now, at the time of dissolution (pralaya) of the cosmos, a reverse process takes place. Some writers have termed it as ‘involution.’ All the products or evolutes merge back into their respective evolutands. The effects merge back into their parent-causes and the entire causal chain rolls back. Finally, the primary causal substance (prakrti) itself rolls back into the Lord. Here comes the metaphor! Isvara, unlike prakrti, is wholly a spiritual personality, not dead matter. Therefore, the Lord Himself can never be a cause (karana) in the manner of the material evolutands mentioned in the preceding lines, into which the primal matter could literally merge back. Thus, this description is merely conceptual or metaphorical. Prakrti, rolls back, as it were, into the supreme cause (parama karana), Narayana. In reality, it goes back to its state of unactuated equilibrium. This is the conceptual model.
Now, coming to the jivas, at the time of the dissolution (which can also be taken to mean the dissolution of the individual body), the unredeemed, matter-like jivas all merge back into prakrti. They remain embedded in a subtle state in prakrti. Considering, in the light of our conceptual model, how close prakrti is to Isvara in this hierarchy of material evolution, can we not say that, at the time of pralaya, the jivas also remain very close to the Lord? Embedded into prakrti—which, in turn, is embedded, as it were, into the Lord, its karana—they are just a single rung away from ‘entering’ into the Lord. They are merged into prakrti, yet not merged into the Lord. So near and yet so far!
But, when the embodied personality takes sole-refuge in the Lord and does pure devotion to Him, he is purified; his consciousness is purified. After death, the limitations (upadhis) of matter or prakrti cleave onto him no more. From the point of view of our conceptual model, we say: he does not enter prakrti again; he has entered directly into the Lord! He has merged into the Lord and not into prakrti!
In reality, as in the case of prakrti, the purusas also do not literally enter into the Lord. They are not literally present within the Lord.
To summarize: the pure personality (purusa) does not literally enter or merge into God on salvation or supreme liberation. They only become pure (suddha)—free from ignorance (avidya); and maintain their (separate) existence as pure spiritual personalities, as the eternal pure devotees of the Lord; in His spiritual abode. They come out of the process of material evolution. When we talk of their merging back into the Lord, it is only as a metaphor, in the context of a certain conceptual model of cause and effect.