"Threshold" - in biblical, figurative meaning - is "beginning", "entrance", "boundary", "border".

"Threshold" of God is a symbol of the initial knowledge of the Will of God, set forth in the Holy Scriptures by the Prophets, Christ and the Apostles, giving man the opportunity to "transcend" his former sinful views, to step over, to leave the sinful way of life and "enter" into a new, righteous life, into the "House", into the "Temple" of God, into the "Church" of God, - into the spiritual Assembly of righteously living people.  

"Threshold" of man is a symbol of his conscience, through which by rejection, perversion of the Will of God, His Commandments, he can "overstep", i.e. commit deviation, crime, impiety, evil.

"Threshold" of man is also a measure of his mental, intellectual abilities and possibilities limited by his physical nature.

"Threshold" of man is also a symbol of various knowledge, false beliefs, false teachings of man, with which he enters into relations with the world around him.