According to Osho, the soul ‘needs’ to dissolve into the Divine because life inherently longs for bliss, not suffering. Separated from the Divine there is misery; in union there is fulfillment. This is not a religious demand but an existential pull: everyone seeks bliss. ‘God’ is the name for total bliss—when no need remains. Dissolution simply means rising from darkness to light, ending craving and thus ending sorrow.
Like a thirsty person needs water, your heart needs real happiness; merging with the Divine is drinking until the thirst ends for good.