"And being thus overcome with the Spirit, he was carried away in a vision, even that he saw the heavens open, and he thought he saw God sitting upon his throne, surrounded with numberless concourses of angels in t he attitude of singing and praising their God."
While Lehi was exhausted by the Spirit he was able to see a vision that god sent to him. Because of this vision Lehi was able to get his family, in the future, safely away form Jerusalem, protecting them from the inevitable destruction of the city. This opened Lehi's eyes to see the glory of God and the blessings from the faith connected to it.
Lehi was one of many to see god on His throne and angels singing praises to the Lord. I personally believe that this is repeated so often as to remind us of the joy in praising the Lord. The heavens opening is also mentioned many times, much like the veil of forgetfulness and separation from God being taken away. Through the opening of the heavens many prophets have seen God in visions. By the power of the Holy Ghost is this possible. As desire to know and understand opens the way for the Spirit to show great things.
This is much like catching glimpses of the eternities with which the angels sing praises of God and prophets and disciples stand on the right hand of God.