The noun οφελος (ophelos) describes an advantageous gain or furtherance of an increase of some specified dynamic accumulation, like a tributary joining a main river, a tribe joining an army, or a payment joining a treasury (1 Corinthians 15:32, James 2:14 and 2:16 only). It comes from the verb οφελλω (ophello), meaning to aid, increase or enlarge, particularly of heaps such as waves that are made larger by a raging wind, or speeches that swell from passion. It may also describe the rushing in of support troops during some military engagement, and secondarily the acquisition of additional booty to add to the spoils of war. It even relates to words in cognate languages that mean broom: an item made from bundled sticks, which is used to sweep up loose debris onto an increasing heap. This verb emphasizes both the effort made and the advantage gained. The verb isn't used in the New Testament but from the noun derive:

The verb οφειλω (opheilo) means to owe or be indebted — whether payment against a debt or proper behavior against a norm: to ought. Indeed, our English word "ought" is a past tense of the same archaic verb that morphed into the modern verbs "to own" and "to owe", which is basically the same verb but in transitive (X owns Y) and intransitive (Y is due) variations. Also note that before the modern age, a person was not so much defined by lofty ideals or fleeting character traits but rather by his possessions: "to hold one's own" means "to keep control over one's properties". This is actually rather insightful, since every human individual derives their personal identity from society at large (we have a personal consciousness because we have words, but language is always a collective thing), society derives its cohesion from its economy and all complex economy derives from property rights. This is perhaps sad but true; an ideal economy may be based on pure love (Song of Solomon 2:4, Romans 13:8) but a less-than-ideal one such as ours must be based on φιλαργυρια, philarguria, or accounting and the keeping of records of incurred debts (1 Corinthians 13:5), which is still better than one based on the supremacy of the fittest.

Our verb οφειλω (opheilo), to owe, is certainly related to οφελλω (ophello), to add to one's holdings (see above), but while the latter speaks of piling up a heap, our verb οφειλω (opheilo) appears to speak of digging a hole. It's an odd inversion, which actually demonstrates that our verb's emphasis is not on the debtor who owes, but rather on the creditor who owns. It furthermore implies that the creditor is not so much interested in any single debtor but rather aims to create an entire environment out of independent debtors, whose unified momentum may be gathered into a "broom of destruction" (in the words of Isaiah 14:23), at the discretion of the creditor.

In deep antiquity, this verb probably predominantly described the perpetual readiness of a militia of subscribed landowners. In modern times it encapsulates the modus operandi of banks. Particularly the latter explains that a debt is incurred when someone sells their future: when someone accepts payment not in exchange for their possessions or service or labor that they already performed, but rather for goods not yet possessed or labor not yet performed or even attentions not yet deserved. And since no one is guaranteed of their own future, and therefore doesn't own it, a debt is incurred when someone sells something that isn't theirs to sell. It's a close cousin of theft.

This verb is used 36 times in the New Testament, see full concordance, and from it derive: