Probably 1978 for the exact wording though phrases like 'law of health' have been used before.
No where can I find extensive or official reference to "the Lord's law of health" beyond
Brigham Young Journal of Discourses (referenced law of health)(1854-86)
Gospel Principles (1978)
The Lord Has Given Us a Law of Health (Ensign 2012)
The Lord Needs you Now (...
The short answer (partly) is yes, they cannot visit the temple. My husband and I lost our temple recommends for not paying tithing (for one year, we paid tithe for around 15 years at this time) and my 16 year old at the time was also questioned about his tithing.
Whether they would definitively say that you can or cannot receive salvation is another story ...
Quotes from MORMON PROPHETS that are considered to be infallible teachings of the LDS
Bruce McConkie (the author of your first three quotes) himself states:
[N]ot every statement made by a Church leader, past or present, necessarily constitutes doctrine. It is commonly understood in the Church that a statement made by one leader on a single occasion ...
Interestingly, Genesis 4: 1 says":
"Now Adam knew Eve his wife, and she conceived and bore Cain, and said, “I have acquired a man from the Lord.” "
The verse does not say that Cain was the first-born child of Eve. We see in other places in Bible, a special mention of the first-born , as in 2 Samuel 3:2:
"Sons were born to David in Hebron: His firstborn ...
In short, it's related to the fact that The Church of Jesus Christ of Latter-day Saints has a lay ministry.
With only very few exceptions, all leaders and teachers in the LDS Church serve in a part-time capacity.
Most members have an official role or "calling," but regardless of their specific current calling, eligible members are ordained to various ...
For what it's worth, the September 1973 New Era magazine (not canon) suggests that it was a mental not physical obstacle:
The scriptures do not say Adam and Eve could not have children; they say Adam and Eve would not have had children if they had remained in a state of innocence, not knowing good from evil.
This scripture seems to indicate that Adam ...
Was Jesus created?
Yes. The Son was created by the Father, both spiritually before the creation of the world, and then later physically when he was born of Mary.
Mankind's spirits were also created the Father, and in that sense LDS doctrine understands Jesus to be the elder spirit brother of mankind.
And if children, then heirs; heirs of God, and joint-...