Claim. God placed cain in the position to relate with Satan (representing evil) and abel in the position to relate with God (representing goodness) because Cain and Abel were the respective fruits of eve’s two fallen acts of love — the first with the Archangel and the second with adam — and the second act was more in line with the principle-of-creation.
Elaboration. Per DP §1.1, Eve’s fall was consummated through two illicit love relationships. The first — sexual union with the archangel — was motivated by excessive desire to “have her eyes opened, like God”; the second — premature union with Adam — was motivated by longing to return to God’s bosom after realizing the first act was wrong. Although both were sinful, the second was more “forgivable” and structurally closer to God’s original design.
Cain, as the first fruit of Eve’s love, carried the signification of her first fallen act; Abel, as the second fruit, carried that of her second. God therefore assigned each son a position dealing with only one master — a structural requirement of the principle-of-creation that humans serve one master. Satan, having seized creation by the Principle of God raising up the eldest, felt stronger attachment to Cain; God therefore dealt with Abel.
DP buttresses this by the OT pattern of God preferring second sons (Jacob over Esau, Ephraim over Manasseh, Levites over other tribes) and striking the firstborn of Egypt. The Cain/Abel positional split is thus not arbitrary divine election but a structural necessity inherited from the dual character of Eve’s fallen love.
See also. Pre-grep: distinct from Ch 2-1’s dp-foundation-of-substance-removes-fallen-nature-via-cain-abel-indemnity (the abstract mechanism) — this atomic gives the operational origin of the positional assignment itself.