Complex sentence: The most important, or at least the most profitable of its properties its ability to assist the Spacing Guild with folding space and is vital to space travel because it allows safe interstellar travel to any part of the universe instantaneously.
Split into simpler sentences: The most important, or at least the most profitable of its properties its ability to assist the Spacing Guild with folding space. The Spice is vital to space travel because it allows safe interstellar travel to any part of the universe instantaneously.