The impersonal aspect [of God] (Nirakara, Nirguna) is called Brahman, or 'unknowable' by Herbert Spencer, 'will' by Schopenhauer, Absolute Noumenon by some 'substance' by Spinoza. The personal aspect (Sakara) of that Being is termed 'Ishvara' or Allah, Hari, Jehova, Father in Heaven, Buddha, Siva, etc. Just as vapour or steam is formless, so also God is formless in His unmanifested or transcendental state.
SivanandaThe real spiritual progress of the aspirant is measured by the extent to which he achieves inner tranquility.
Sivananda