1st Nephi 3:7 says that the Lord does not give a commandment unto the children of men, save He prepares a way for them to accomplish it. Yet D&C 124:49 says that when our enemies prevent us from accomplishing one of the Lord’s commandments, He no longer requires it of us. So how can both verses be true? If Nephi had had D&C 124:49, would he not have been justified in giving up after his first two failures to get the brass plates?
Your second question is answered by my response to a very similar question way back in 2007. Essentially, both verses make it clear that we are obliged to do all in our power to obey unless or until the Lord says otherwise. What I wrote there very much applies to your first question as well. I think it’s important that we look at the exact text of both verses:
1 Nephi 3:7 And it came to pass that I, Nephi, said unto my father: I will go and do the things which the Lord hath commanded, for I know that the Lord giveth no commandments unto the children of men, save he shall prepare a way for them that they may accomplish the thing which he commandeth them.
D&C 124:49 Verily, verily, I say unto you, that when I give a commandment to any of the sons of men to do a work unto my name, and those sons of men go with all their might and with all they have to perform that work, and cease not their diligence, and their enemies come upon them and hinder them from performing that work, behold, it behooveth me to require that work no more at the hands of those sons of men, but to accept of their offerings.
There are a few things we can consider regarding the apparent conflict:
Modern Prophets and the Gift of the Holy
These apparent conflicts are one reason we have modern prophets and apostles to help us put into our own context what past prophets and apostles have said. The gift of the Holy Ghost is also intended to guide us in our own lives to know how we should proceed in a specific instance, or how to understand and apply scripture.
Intent of the Commandment
We may not always know the intent of the commandment, nor the reason it was revoked, but there are some interesting historic examples: Abraham was commanded to sacrifice Isaac. When the Lord did this, He knew He would not allow this command to be completed, yet He commanded it anyway. At least two purposes seem clear: first to test Abraham’s faith (and presumably Isaac’s), and second to provide a symbol and testimony regarding Christ’s Atonement. In this case, the commandment was revoked because the intended purposes had been met. Sometimes, the Lord asks us to do things as a test, or to give us the opportunity, rather than because the thing itself must be accomplished.
In another case, the children of Israel lost the higher law, and were given a lesser law, because they so quickly turned to sin (while Moses was on mount Sinai receiving the higher law), thereby showing they weren’t ready. In this case, the law was revoked due to sin (and while this was not good for the children of Israel, I personally believe it was better for them than if they had received and then violated the higher law).
In the case mentioned in D&C 124, the saints had been told to build a temple in Missouri, but failed to do so. While the failure can be blamed on their enemies, it’s possible some of those enemies were among the saints themselves. That is, building a temple was something the entire group was expected to do together (and it would have been near impossible for only a few to do it). If some chose not to, or weren’t diligent in their efforts, this could cause the group as a whole to fail, even though many were indeed diligent. I think this phrase: “and those sons of men go with all their might and with all they have to perform that work, and cease not their diligence” is critical in understanding the verse. Those who gave their all are excused and their efforts accounted as righteousness. Those who did not give their all may not be able to say the same thing.
And that takes us to the question of context, which is critical in understanding the intent of scripture.
In Nephi’s case, the command had to be accomplished or generations of people would suffer. Indeed, it might have been pointless to take Lehi’s family to the promised land without the brass plates. In the case of the early saints, while we can be certain they would have been blessed for completing a temple, we also know that things have turned out pretty well for the saints in spite of this failure, regardless of its cause. More importantly, we know that Nephi did all he could, and so the Lord helped him. Contrastingly, in the timeframe in which D&C 124 was given, there were members who were turning away, and even betraying their fellow saints. In this case, perhaps the commandment had served sufficient purpose.
Finally, details and language matter. 1 Nephi 3:7 says the Lord will “prepare a way” that we “may accomplish” the command. It doesn’t say we are always going to take the prepared way, or even recognize it. Nephi was able to act alone, and clearly followed the prepared way with full intent. In building a temple, the saints had to be united, and earlier verses (especially verse 45) make it clear had they done that, they would not have been “moved out of their place”. It appears that the way was prepared, but since too few chose the way, the command was revoked and those who had been diligent were excused.
Like Nephi, I know that the Lord will prepare ways for us to be obedient. It is up to us to choose whether we will follow the prepared way.