'Swear' in the Bible

In that day five cities in the land of Egypt will speak the language of [the Hebrews of] Canaan and swear allegiance to the Lord of hosts. One [of them] will be called the City of Destruction.

“I have sworn [an oath] by Myself,The word is gone out of My mouth in righteousnessAnd shall not return,That to Me every knee shall bow, every tongue shall swear [allegiance].

“Hear this, O house of Jacob, you who are called by the name of IsraelAnd who come from the seed of Judah,You who swear [allegiance] by the name of the LordAnd invoke the God of Israel,But not in truth (sincerity) nor in righteousness [with moral and spiritual integrity].

“Because he who blesses himself on the earthWill bless himself by the God of truth and faithfulness;And he who swears [an oath] on the earthWill swear by the God of truth and faithfulness;Because the former troubles are forgotten,And because they are hidden from My sight.