Oneness does not mean singleness, but rather it implies two or more. The Lord said that “I and my Father are one” (John 10:30). Hence at least two, plural and not singleness of person’s or in this case a single God, but Gods plural who share a oneness, one purpose.
One(ness) heart and one(ness) mind, is oneness, and not singleness, but there is much more to this simple phrase, and also many more.
As we see in the scriptures the term one church, or one fold, all mean oneness but out of many — this also has the same implications with other terms such as one flesh, there being at least two, a husband and wife. As it is with God, and His family, it is one family which consists of many and these are who are the Church of the First Born, where all are First Born Sons and Daughters of God. It is a covenantal relationship establishing all the rights and privileges for an inheritance and a continuation of Gods seed, forever and ever.
“And he that receiveth my Father receiveth my Father’s kingdom; therefore all that my Father hath shall be given unto him.” (D&C 84:38/John 16:15)
Oneness, one heart, and one mind is not just a state of being or place in which we seek to obtain harmony with one another or purpose, or enlightenment from on high nor is it even a peace of mind, it is also not wordplay either or semantics, Fatherly advice, etc. Rather, it is God establishing His laws among mankind. Therefore the term to be “one” is a legal or covenantal term and a commandment.
“And they twain shall be one flesh” (KJV Mark 10:8)
One flesh can be best understood if referred to as a legal term also. It is a covenantal term, and in this case “one flesh” is establishing the covenant and laws of God concerning marriage, the union of a man and a woman. In more simpler terms, one flesh means a marriage between a husband and a wife of full legal status according to the laws of God. In Biblical times this would have been called a rabbinical marriage, as layed out in the scriptures. Gods laws establish equity in the marriage, neither one ruling over the other. Such as Adam and Eve, they being equal in power and strength. They had equity and were created in the express image and likeness of God, plural, both male and female (Gen 1:27). Whereas a half marriage or marriage of lesser status is an offense to God, an abomination and it offends the hearts of the innocent.
One flesh really has nothing to do with sex, sexuality, or one wife or one husband; but this is the conclusion for many when looking very narrowly at a single passage of scripture ignoring the context of what is being taught here and throughout scripture. Rather one flesh establishes the laws of God and the associated rights, privileges, honors, glories, duties and ramifications for violation of any part of the marriage covenant, to which one in this instances has full claim upon the other not just for themselves but also for any progeny produced through the course of the marriage forever more, from generation to generation. Whereas as a half marriage or marriage of lesser status, does not.
The Father and Son are one, the wife and husband are to be one, and we are to be one with one another and also with God. It comes full circle. Hence the commandment to have all things in common, and having no rich or poor among us, and these in that day shall not say know ye the Lord, for all shall know the Lord and He shall be with them, for they all are one in Him and if one in Him they are also one with the Father, and the Father with them. For they all are one and they together with Christ joint heirs of salvation having a fullness. (John 17:21, 23)
“if ye are not one ye are not mine” (D&C 38:27)
Come unto Christ and repent, if you are one with Christ then you can be one with each other.