A lot vs. Alot: 9 Grammatical Pitfalls
Old English að "oath, judicial swearing, solemn appeal to deity in witness of truth or a promise," from Proto-Germanic *aithaz (cf. Old Norse eiðr, Swedish ed, Old Saxon, Old Frisian eth, Middle Dutch eet, Dutch eed, German eid, Gothic aiþs "oath"), from PIE *oi-to- "an oath" (cf. Old Irish oeth "oath"). In reference to careless invocations of divinity, from late 12c.
a solemn appeal to God, permitted on fitting occasions (Deut. 6:13; Jer. 4:2), in various forms (Gen. 16:5; 2 Sam. 12:5; Ruth 1:17; Hos. 4:15; Rom. 1:9), and taken in different ways (Gen. 14:22; 24:2; 2 Chr. 6:22). God is represented as taking an oath (Heb. 6:16-18), so also Christ (Matt. 26:64), and Paul (Rom. 9:1; Gal. 1:20; Phil. 1:8). The precept, "Swear not at all," refers probably to ordinary conversation between man and man (Matt. 5:34,37). But if the words are taken as referring to oaths, then their intention may have been to show "that the proper state of Christians is to require no oaths; that when evil is expelled from among them every yea and nay will be as decisive as an oath, every promise as binding as a vow."
sacred or solemn voluntary promise usually involving the penalty of divine retribution for intentional falsity and often used in legal procedures. It is not certain that the oath was always considered a religious act; such ancient peoples as the Germanic tribes, Greeks, Romans, and Scythians swore by their swords or other weapons. These peoples, however, were actually invoking a symbol of the power of a war god as a guarantee of their trustworthiness.