Luke 6:39

(de Qu. Ev. l. ii. q. 9.) Or, He has added the words, Can the blind, lead the blind, in order that they might not expect to receive from the Levites that measure of which He says, They shall give into thy bosom, because they gave tithes to them. And these He calls blind, because they received not the Gospel, that the people might the rather now begin to hope for that reward through the disciples of the Lord, whom wishing to point out as His imitators, He added, The disciple is not above his master.

The Lord added to what had gone before a very necessary parable, as it is said, And he spake a parable to them, for His disciples were the future teachers of the world, and it therefore became them to know the way of a virtuous life, having their minds illuminated as it were by a divine brightness, that they should not be blind leaders of the blind. And then he adds, Can the blind lead the blind? But if any should chance to attain unto an equal degree of virtue with their teachers, let them stand in the measure of their teachers, and follow their footsteps. Hence it follows, The disciple is not above his master. Hence also Paul says, Be ye also followers of me, as I am of Christ (1 Cor. 1:11.). Since Christ therefore judged not, why judgest thou? for He came not to judge the world, but to show mercy.

Or else, If thou judgest another, and in the very same way sinnest thyself, art not thou like to the blind leading the blind? For how canst thou lead him to good when thou also thyself committest sin? For the disciple is not above his master. If therefore thou sinnest, who thinkest thyself a master and guide, where will he be who is taught and led by thee? For he will be the perfect disciple who is as his master.