अभ्यासेऽप्यसमर्थोऽसि मत्कर्मपरमो भव। मदर्थमपि कर्माणि कुर्वन् सिद्धिमवाप्स्यसि ॥

abhyāse ’py asamartho ’si mat-karma-paramo bhava mad-artham api karmāṇi kurvan siddhim avāpsyasi

If also thou art not equal to constant practice, be intent on My service; performing actions for My sake, thou shalt attain perfection.

In plain words: Krishna says that if even regular practice is too hard, Arjuna should focus on serving him and do his work for Krishna's sake. That way he will still reach perfection.