‘Hypostatic’ is from the Greek ‘en,’ meaning “in,” and ‘hypostasis,’ meaning “substance.” The incarnate Christ has two natures (undiminished deity and true humanity), inseparably united without loss of separate identity in one person forever. Hypostatic union is the theological term for the incarnate Person of Christ. It refers to the union of God and man.
Christ, the God-man, unites in Himself the Essence of God and the essence of man — therefore, only Christ was ever qualified to be the judicial mediator between God and man. The fact that a mediator must be equal with the parties involved makes Christ the only person who could qualify to save mankind.
R.B. Thieme, Jr. said it well: “In the Person of the incarnate Christ are two natures, Divine and human, inseparably united without loss or mixture of of separate identities, with out loss or transfer of properties or attributes, the union being personal (the God-man is one Person) and eternal Christ will be the God-man forever). From the book Christian Integrity, pp210-14.
Explanation: At the virgin birth, God the Son took upon Himself true humanity and became (the new) Person — the God-man, the Unique Person of the Universe (John 1:1-14; Romans 1:2-4; Philippians 2:5-11; 1 Timothy 3:16).
‘Hypostasis’ means “essence or actual being; it means “reality.”
“Christ is in actuality – reality!” — C.S. Craig.
The deity of Christ as God (the Son of God) are synonymous terms — Christ is God, the second person of the trinity. Therefore, Christ is the unique person in the Universe — the God-man. Undiminished deity took upon Himself true humanity in order to become the Savior (Hebrews 2:14-15; Philippians 2:7-8), the mediator between God and man (Job 9:2, 32-33; 1 Timothy 2:5-6), the great high priest representing man before God (Hebrews 7:4-5, 14, 28; 10:5, 10-14), and the human King of Israel in fulfillment of the Davidic Covenant (2 Samuel 7:8-16; Psalms 89:20-37).
Please note that the hypostatic union of God and man began at the incarnation of Jesus Christ — a babe in a manger born of a virgin, born with out a human father, therefore NO sin, without stain. Christ met the judicial requirement of “mediator.”
See “Mediator.”