"For my people have committed two evils; they have forsaken me the fountain of living waters, and hewed them out cisterns, broken cisterns, that can hold no water." (Jeremiah 2:13)
"And if he be not able to bring a lamb, then he shall bring for his trespass, which he hath committed, two turtledoves, or two young pigeons, unto the Lord; one for a sin offering, and the other for a burnt offering." (Leviticus 5:7)
The verse from Leviticus refers to the specific Old Covenant atonement for several things, one of which was, how can I say this, "speaking an oath". A couple verses prior does it explain how it doesn't matter what the oath was or whether or not one was sincere in uttering it. If it was for good (in their mind) or not, should that utterance be one of "foolishness" (5:4 NLT), and then after it is revealed to the utterer, two birds up and lose their life.
A bird in the hand
"Vow, and pay unto the Lord your God..." (Psalm 76:11a)
God marks our words. Let fly some random comment that speaks to a base part of your life (something affecting you on a deep level) and unless His mercy intervenes, you'll be hemmed in by what you said. It could very well be something of good intent but if it didn't line up with God's logic, it's sin. After meeting with my pastor's wife one Autumn day for something altogether different, we ended praying against a vow I'd taken God knows when that I didn't even know was affecting me.
An oft-cited tale of strict vow-keeping is that of Jephthah. "For I have opened my mouth unto the Lord, and I cannot go back." (Judges 11:35b) Thing is, he promised God he'd offer as a sacrifice the first thing that "cometh forth of the doors of my house to meet me" (11:31). And then his daughter meets him on the doorstep. In doing her best to keep with the vow, she forswears her virginity to God. Pretty serious as well but at least she retained her life. God takes our promises seriously.
"But I say unto you, Swear not at all... But let your communication be, Yea, yea; Nay, nay: for whatsoever is more of these cometh of evil." (Matthew 5:34a, 37)
No stone unturned
"Set a watch, O Lord, before my mouth; keep the door of my lips." (Psalm 141:3)
I find numerous times when I open my mouth to say what just bubbled up to the tip of my tongue does the Holy Spirit check. A simple impulse that, were it worded in English would be something akin to "wait". "Stop." "Don't." At the risk of looking like a stuttering fool do I (sometimes reluctantly) hold my tongue and let the conversation lag. It is very important we know God loves us but also that we ensure the words we speak are all in line with God's plan. If you think about it (literally), the outworking of God's plan in your and my life goes from thoughts to words to deeds. This could very well be one of the reasons Nehemiah (2:12) says "neither told I any man what my God had put in my heart to do at Jerusalem." Accusations, misunderstanding, misinterpretation. All things allayed by keeping one's mouth shut and speaking to God. As the devil is the "accuser of our brethren" (Revelation 12:10), best not to give him ammunition to go to work.
"For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries." (1 Corinthians 14:2)
In closing, the word "diglossia" refers to different types of the same language spoken in the one region. The top verse from Jeremiah speaks of "two evils". In keeping with the concept of duality with the sacrifice of "two turtledoves" or "young pigeons", look to the Holy Spirit (He's like a dove—one dove). He has a language all His own and if you feel so inclined ask Him to give you a piece of the gift of tongues. Don't think weird noises that make you sound like a fool and act like one too. But don't shut Him off from the delivery of information by means other than what you're accustomed to or that you might expect. (Diglossia also refers to the cleft or forked tongue of, say, a snake.) Only that information (for lack of a better word) from the throne of God and mixed with our heart should be spoken by us, being His children.
"For it shall be given you in that hour what ye shall speak. For it is not ye that speak, but the Spirit of your Father which speaketh in you." (Matthew 10:19