Galatians 6:9 exhorts us not to grow weary while doing good. We are promised that we will reap in due season as long as we do not give up or ‘faint’. Albert Barnes comments on the need for perseverance:
It is implied here, that unless a man perseveres in doing good to the end of life, he can hope for no reward. He who becomes disheartened, and who gives over his efforts; he that is appalled by obstacles, and that faints on account of the embarrassments thrown in his way; he that pines for ease, and withdraws from the field of benevolence, shows that he has no true attachment to the cause, and that his heart has never been truly in the work of religion. He who becomes a true Christian, becomes such FOR ETERNITY. He has enlisted, never to withdraw. He becomes pledged to do good and to serve God always. No obstacles are to deter, no embarrassments are to drive him from the field. With the vigor of his youth, and the wisdom and influence of his riper years; with his remaining powers when enfeebled by age; with the last pulsation of life here, and with his immortal energies in a higher world, he is to do good. For that he is to live. In that he is to die; and when he awakes in the resurrection with renovated powers, he is to awake to an everlasting service of doing good, as far as he may have opportunity, in the kingdom of God.