People with antibodies (assuming the test works and is specific enough) may have cleared the infection already and they may enjoy (temporary?) immunity enough f

People with antibodies (assuming the test works and is specific enough) may have cleared the infection already and they may enjoy (temporary?) immunity enough for them to resume a part of their activities in a lockdown. The other goal, as others have said, is to isolate, and contact trace the infected. And I add, early detection might also help with treatment, since the scant evidence so far suggests that pharmacological interventions that target the virus might be more effective early on during the infection.