Luther, under the influence of Augustine’s teaching, suggested sin as “Incurvarus in se”. While Augustine suggested that our primary sin can be understood as pride and a misplaced love, that is, self-love, Luther expanded on these ideas that sin is actually “humanity curved inward on itself”. In sin, humans live inwardly as solitary beings instead of communal beings. What a great insight.
Humanity was made in the image of triune God. We outflow love to others as those receive love from God. It is an outward living rather than an inward living.