Probably one of the greatest theologians of our time, Carl F.H. Henry, citing John Calvin, writes:
The knowledge of God is nonetheless for the sake of the good life.
"We are invited to a knowledge of God not such as, content with empty
speculation, merely floats in the brain, but such as will be solid and
fruitful, if rightly received and rooted in out hearts" (Institutes
I, 5, 9). The pious mind covets knowledge of God for the sake of
reverent worship and obedience. "The right way, and the best method
of seeking God" is "not with presumptuous curiosity to attempt an
examination of his essence, which is rather to be adored than too
curiously investigated; but to contemplate him in his works, in which
he approaches and familiarizes, and, in some measure, communicates
himself to us" (Ibid, I, 5, 9). "Cold and frivolous . . . are the
speculations of those who employ themselves in disquisitions on the
essence of God, when it would be more interesting to us to become
acquainted with his character, and to know, what is agreeable to his
nature" (Ibid. I, 2, 2).
In other words, "Don't look for God to take a shower." Or, better, "Don't peak at God lounging poolside."
(I would highly recommend Henry's work in Christian theology, God, Revelation, and Authority [in five volumes: 1976-1987]. He address the problem of Thomastic theology, at least partly, in his Chapter 20: "The Theological Transcendent A Priori," Volume 1.)
Nevertheless, Plato's concept of 'Form' or 'eternal substance' (eidos) is related significantly to 'essence' (ousia); also, hypostasis is substantial, concrete being between the merely actual but contingent and the realities that are merely mental. The whole picture is a 'tricotomy':
mental reality (appearance)
hypostasis: concrete being (substance)/becoming (change): 'reality'
actuality by contingency (hypokeimenon): the basic primary matter which has not yet been formed: a circling back to the
original Form (Ideal). (In successful philosophy and
philosophic-theologic world-life views: that which is placed in the
lower story does not consume the upper (as in modernism and postmodernism); rather, it merges with it.
Watch for this.)
Historic or personal movement through time begins 'top-to-down'. Reality and appearance are sometimes opposed. Time (to the Platonists and Neo-Platonists) was thought of as noema (thought or concept) and metron (measure), but not as hypostasis (the reality we experience; with this in mind, you might detect how C. Godel [Einstein's best friend] was merely a Neo-Platonist).
Hypostasis is further identified with the world spirit or world soul. It is 'essence' that gives stability to the concrete, individual thing. This is the world of substantia (substance: electrons, protons, neutrons and stuff; This is my, your world; the objective world).
Plato's 'Form' basically meant "to place under." Under what? Under heaven, God's realm. Our world is both under heaven literally and by authority (the Creator's conduct). Our world is like a world under water... a bottom world upon which one can or cannot get a foothold. It's like 'night-floundering' in Georgia swamp land, a lantern and a 'gig' in-hand. You look, feel for solid ground under and through the deep dark, dank forested swamp waters. Sometimes nothing is there, so you float. Or, you tread water (with all that stuff in both hands, better tread with your feet)! Sometimes you might feel with your bare feet the muddy bottom ooze. Yea, "That's 'bottom'." Tillich's "God, the ground of all being."
(I would highly recommend The New International Dictionary of New Testament Theology [1967; 1975], Volume 1: s.v., "Form," p. 703-714.)