The child of God is like a lame man that goes the right way, but yet halts at every step. Abraham and Sarah desire issue, that is from the Spirit; but they desire issue by Hagar their handmaid, that is from the flesh. Rebekah seeks the blessing for Jacob, that is a work of the Spirit; but she seeks it by lying, that is from the flesh. Peter eats with the Gentiles, that is from Christian liberty. He afterwards separates himself, that is from corruption. Thus we see that the best works are imperfect and mixed with corruption, and that for the best works we must humble ourselves and seek pardon, not in respect of the goodness of the work, but in respect of the defect thereof.William Perkins, Commentary on Galatians, in Works, 2:103 (HT: Inwoo Lee).