The Supreme Absolute
"Even the greatest philosophical speculators cannot have access to the region of the Lord. It is said in the Upanisads that the Supreme Truth, the Absolute Personality of Godhead, is beyond the range of the thinking power of the greatest philosopher. He is unknowable by great learning or by the greatest brain. He is knowable only by one who has His mercy. Others may go on thinking about Him for years together, yet He is unknowable."
Srimad-Bhagavatam 1:8:20 Purport

Understanding the Absolute Truth, the Supreme Personality of Godhead, may be approached in various ways. For example, Absolute Truth may be realized in three features known as para-tattva: impersonal Brahman, localized Paramatma, and Bhagavan, the Supreme Personality of Godhead. The Lord is impersonal, personal and localized. By His impersonal feature He is all-pervading Brahman, by His localized feature He is present in everyone's heart as the Supreme Soul (Paramatma), and by His ultimate personal feature (Krsna) He is the object of transcendental loving service by His fortunate associates, the pure devotees.
The Supreme Being's manifest form is explained in the Vedas as sat-cit-ananda vigraha, "an embodiment (vigraha) of absolute eternity (sat), absolute cognizance (cit), and absolute bliss (ananda)." Impersonal Brahman realization is the realization of His sat (being) feature. Paramatma realization is the realization of cit (eternal knowledge). But realization of the Personality of Godhead, Krsna, is realization of all the transcendental features: sat, cit and ananda (being, knowledge, bliss) in complete vigraha (form).
The Absolute Personality may also be understood as the perfect person who has manifold energies, out of which the internal, external and marginal energies are primary. The spiritual world is the manifestation of the Lord's internal potency. By expanding his internal energies, He manifests as so many personalities, and exchanges or accepts transcendental loving service from them in the spiritual world. The material world is the manifestation of His external potency. The living entities are manifestations of His marginal potency, and by their own choice they can live in either the transcendental or material worlds.