Joint Heirs

This is one of the wildest ideas that the LDSaints put forth. They believe that all of us are children of God and therefore all of us are heirs of God. This, to them, means that we can become gods, as suggested in other comments. You can see that one idea does not follow from the other.

LDSaints point out that Romans 8:17 proves their claim. We can see that a closer look is required.

And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.

Key is the IF in "if we are children. Who are the children referred to? Everybody? or is the title more limited than LDSaints would like.

14. For as many as are led by the Spirit of God, they are the sons of God.
15. For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.
16. The Spirit itself beareth witness with our spirit, that we are the children of God:
17. And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.

We see that not everybody is a child or son of God. We see that only those who are led by the spirit are. Indeed, even those who are led by the spirit are only sons of God by adoption. Adoption would be superfluous if we were literal offspring of God.

The Book of Mormon supports this idea of "becoming" children of God.

Mosiah 5:7 And now, because of the covenant which ye have made ye shall be called the children of Christ, his sons, and his daughters; for behold, this day he hath spiritually begotten you; for ye say that your hearts are changed through faith on his name; therefore, ye are born of him and have become his sons and his daughters.

I would suggest that if your Church does not teach this they are preaching a different gospel than that taught by Christ. Even He didn't consider, as LDSaints do, that everyone is His brother and sister.

Matthew 12

46. While he yet talked to the people, behold, his mother and his brethren stood without, desiring to speak with him.
47. Then one said unto him, Behold, thy mother and thy brethren stand without, desiring to speak with thee.
48. But he answered and said unto him that told him, Who is my mother? and who are my brethren?
49. And he stretched forth his hand toward his disciples, and said, Behold my mother and my brethren!
50. For whosoever shall do the will of my Father which is in heaven, the same is my brother, and sister, and mother.

“Men become sons of God in the day that the Spirit leads them to believe on Jesus Christ for salvation, and not before. What says the Epistle to the Galatians? "Ye are all the children of God by faith in Christ Jesus." (Galatians iii. 26.) What says the first Epistle to the Corinthians? "Of Him are ye in Christ Jesus." (First Corinthians i. 30.) What says the Gospel of John? "As many as received Christ, to them gave He power (or privilege) to become the sons of God, even to them that believe on His name." (John i. 12.) Faith unites the sinner to the Son of God, and makes him one of His members. Faith makes him one of those in whom the Father sees no spot, and is well-pleased. Faith marries him to the beloved Son of God, and entitles him to be reckoned among the sons. Faith gives him "fellowship with the Father and the Son." (First John i. 3.) Faith grafts him into the Father's family, and opens up to him a room in the Father's house. Faith gives him life instead of death, and makes him, instead of being a servant, a son. Show me a man that has this faith, and, whatever be his church or denomination, I say that he is a son of God”. - J.C. Ryle,

Ye are Gods

Some like to quote “Jesus answered them, Is it not written in your law, I said, Ye are gods?” John 10:34. This, in their mind, proves that we can become gods by inheriting God's godhood! We see, however, that Jesus was telling the Pharisees that they were gods right then and there. He wasn't teaching that someday thy might be gods. Were there gods standing before Jesus? Not is the way LDSaints would have you see.

Reading the segment that Jesus was quoting, we see that they were gods in that they were put in a position of authority. The Psalmist was condemning them for failing to do what righteous leaders, or gods, should do.

Psalms 82

1. GOD standeth in the congregation of the mighty; he judgeth among the gods.
2. How long will ye judge unjustly, and accept the persons of the wicked? Selah.
3. Defend the poor and fatherless: do justice to the afflicted and needy.
4. Deliver the poor and needy: rid them out of the hand of the wicked.
5. They know not, neither will they understand; they walk on in darkness: all the foundations of the earth are out of course.
6. I have said, Ye are gods; and all of you are children of the most High.
7. But ye shall die like men, and fall like one of the princes.

Another sense of "gods" is seen in knowing good from evil and the ability to choose between them.

2 Nephi 2:18 ....ye shall be as God, knowing good and evil.

Alma 12:31 ... becoming as Gods, knowing good from evil, placing themselves in a state to act, or being placed in a state to act according to their wills and pleasures, whether to do evil or to do good--

Alma 42:3 Now, we see that the man had become as God, knowing good and evil;

So we are adopted to be children of God. We are not offspring of Heavenly Parents. The Book of Mormon teaches repeatedly that Adam and Eve were our "first parents" indicating that, well, there were no parents before.

1 Nephi 5:11 And he beheld that they did contain the five books of Moses, which gave an account of the creation of the world, and also of Adam and Eve, who were our first parents;

2 Nephi 2:15 …and to bring about his eternal purposes in the end of man, after he had created our first parents, and the beasts of the field and....

2 Nephi 9:9 And our spirits must have become like unto him, and we become devils, angels to a devil, to be shut out from the presence of our God, and to remain with the father of lies, in misery, like unto himself; yea, to that being who beguiled our first parents....

Mosiah 16:3 For they are carnal and devilish, and the devil has power over them; yea, even that old serpent that did beguile our first parents...

Alma 12:21 What does the scripture mean, which saith that God placed cherubim and a flaming sword on the east of the garden of Eden, lest our first parents should enter and partake of the fruit...

Alma 12:26 And now behold, if it were possible that our first parents could have gone forth and partaken of the tree of life...

(See Alma 42:2, Alma 42:7, Helaman 6:26, Ether 8:25)

Heirs to the Kingdom

Somehow LDSaints assume that being heirs means becoming gods. We see what they are heirs to in the Book of Mormon and it isn't godhood. I am going to quote many verses just so you can see what is to be inherited. You will find nothing about inheriting godhood. I restrict my quotes to the Book of Mormon. You can skip to the Conclusion.

Mosiah 15:11 ....these are his seed, or they are the heirs of the kingdom of God.

4 Nephi 1:17 ....they were in one, the children of Christ, and heirs to the kingdom of God.

2 Nephi 9:18 But, behold, the righteous, the saints of the Holy One of Israel, they who have believed in the Holy One of Israel, they who have endured the crosses of the world, and despised the shame of it, they shall inherit the kingdom of God,

Mosiah 27:26 And thus they become new creatures; and unless they do this, they can in nowise inherit the kingdom of God.

Alma 5:51 And also the Spirit saith unto me, yea, crieth unto me with a mighty voice, saying: Go forth and say unto this people--Repent, for except ye repent ye can in nowise inherit the kingdom of heaven.

Alma 5:58 For the names of the righteous shall be written in the book of life, and unto them will I grant an inheritance at my right hand.

Alma 7:14 Now I say unto you that ye must repent, and be born again; for the Spirit saith if ye are not born again ye cannot inherit the kingdom of heaven;

Alma 9:12 Behold, now I say unto you that he commandeth you to repent; and except ye repent, ye can in nowise inherit the kingdom of God.

Alma 11:37 And I say unto you again that he cannot save them in their sins; for I cannot deny his word, and he hath said that no unclean thing can inherit the kingdom of heaven; therefore, how can ye be saved, except ye inherit the kingdom of heaven? Therefore, ye cannot be saved in your sins.

Alma 39:9 Now my son, I would that ye should repent and forsake your sins, and go no more after the lusts of your eyes, but cross yourself in all these things; for except ye do this ye can in nowise inherit the kingdom of God.

Alma 40:26 But behold, an awful death cometh upon the wicked; for they die as to things pertaining to things of righteousness; for they are unclean, and no unclean thing can inherit the kingdom of God;

Alma 41:4 And if their works are evil they shall be restored unto them for evil. Therefore, all things shall be restored to their proper order, every thing to its natural frame--mortality raised to immortality, corruption to incorruption--raised to endless happiness to inherit the kingdom of God,

3 Nephi 11:33 And whoso believeth in me, and is baptized, the same shall be saved; and they are they who shall inherit the kingdom of God.

3 Nephi 11:38 And again I say unto you, ye must repent, and be baptized in my name, and become as a little child, or ye can in nowise inherit the kingdom of God.

Ether 12:32 And I also remember that thou hast said that thou hast prepared a house for man, yea, even among the mansions of thy Father, in which man might have a more excellent hope; wherefore man must hope, or he cannot receive an inheritance in the place which thou hast prepared.

Ether 12:34 And now I know that this love which thou hast had for the children of men is charity; wherefore, except men shall have charity they cannot inherit that place which thou hast prepared in the mansions of thy Father.

Conclusion

LDSaints have the nasty habit of taking a single verse and running it down the road in a disjointed fashion. They read "spirits in prison" and create some kind of spirit school between death and the resurrection where the evil may repent and move into paradise, etc. They take a reference about some apostates baptizing for the dead and create a whole system of genealogy and temple work for the dead. They take Paul's illustration of Celestial Bodies and Terrestrial Bodies and create a whole system of eternal destinations where God saves and glorifies all the works of His hands. And so they have taken Romans 8:17 and have woven a whole doctrine of deification.