"Wherefore, the Lord hath commanded me that thou and thy brothers should go unto the house of Laban, and seek the records, and bring them down hither into the wilderness."
The Lord knew the importance of the records and commanded Lehi's sons to get them and bring them back to be preserved for later generations. The way to get the plates was not revealed, so this became a huge trial of faith. They had to totally rely on the Lord for a way to obtain the plates.
Lord Himself know plates important, whew, Lehi his sons get plates need. Why? Save for generation. Get plates how? Don't know. Trial itself depend what? Faith. Them rely Lord whole need.