Alma 12:32

therefore God gave unto them commandments, after having made known unto them the plan of redemption, that they should not do evil, the penalty thereof being a second death, which was an everlasting death as to things pertaining unto righteousness; for on such the plan of redemption could have no power, for the works of justice could not be destroyed, according to the Supreme goodness of God.

So God gave them commands after he told them about his plan to save them. He told them not to do evil. The punishment for doing evil is a second death. This is a death that lasts forever as to anything good. The plan to save people can’t work for those who keep doing evil. God’s justice must be done, because God is completely good.

“So God gave them commandments after revealing the plan of redemption. He told them not to do evil, warning that the penalty would be a second death—an everlasting spiritual death. The plan of redemption can’t help people who face that, because justice can’t be overruled. God’s supreme goodness requires it.