The covenantal relationship God established with Adam in Genesis 1-3. Reformed theology distinguishes two phases: the Covenant of Works (before the Fall) and the Covenant of Grace inaugurated immediately after (Genesis 3:15, the protoevangelium). Hosea 6:7 — "like Adam they transgressed the covenant" — strongly implies that the pre-Fall arrangement was formally covenantal even though the word berith is not used in Genesis 2. The stipulation was simple: "Of every tree of the garden you may surely eat, but of the tree of the knowledge of good and evil you shall not eat, for in the day you eat of it you shall surely die" (Gen 2:16-17).
Adam stood as federal head — his actions covenantally represented all his posterity. When he fell, humanity fell in him (Romans 5:12-19, 1 Corinthians 15:22). The stakes were cosmic: eternal life for obedience, death for disobedience. This is why Adam is called "a type of the one who was to come" (Romans 5:14) — Christ stands as the second Adam, federal head of a new humanity, achieving by active and passive obedience what the first Adam failed to secure. The Adamic covenant frames everything downstream: original sin is a covenantal category (imputed guilt and corrupted nature through our covenant head), and justification is a covenantal category (imputed righteousness through our new covenant head). Without federal headship in Adam, the gospel's logic of federal headship in Christ collapses. Both stand or fall together.