Mormons, can you explain another contradiction between the Book of Mormon and the D&C?

God didn't change the situation did. If you read in the section heading to Doctrine and Covenants you find out that the people in question were unable to go when they were originally told to, and so God told us that He will take our strengths and weakness into account in his dealings with us. I see no contradiction there. I only see a testament to God's knowledge and understanding.