Complex sentence: Antennas for repeater work are almost always vertically polarized since 2-meter antennas on cars are usually vertically polarized allowing for maximum signal coupling which equates to stronger signals in both directions.
Split into simpler sentences: Antennas for repeater work are almost always vertically polarized since 2-meter antennas on cars are usually vertically polarized. Matching polarization allows for maximum signal coupling which equates to stronger signals in both directions.