The support of the rope is intended to eliminate the likelihood of a fall altogether, but a backup fall arrest system (Personal protective equipment) is used in case of the unlikely failure of the primary means of support. This redundancy system is usually achieved by using two ropes - a working line and a safety line.
The primary aim of rope support is to completely prevent falls from happening, but a supplementary safety net is implemented in case the main support system fails. This is usually accomplished by utilizing two ropes: one for actual support and another as a backup.