Luke 6:43

For a good tree bringeth not forth corrupt fruit
The particle, "for" is left out in the Syriac, Arabic, Persic, and Ethiopic versions; and so it is in Beza's ancient copy: nor do these words stand in close connection with the preceding in Matthew's Gospel, though they may be very well considered as an illustration of them; for as that cannot be called a good tree, which brings forth bad fruit; so such men cannot be accounted good men, let them make ever so large pretensions to such a character, who are very busy in espying, discovering, and censuring the faults of their brethren; when they take no notice of, nor refrain from, nor relinquish their own. These words, with what follow in this, and the next verse, and the similes in them, are used by our Lord in Matthew, on account of false prophets or teachers; where he suggests, that as good and faithful ministers of the Gospel cannot, and do, not bring forth, and publish corrupt notions, and false doctrines, usually and knowingly; even usual, nor can it be, that a good tree should bring forth corrupt fruit; so,

neither doth a corrupt tree bring forth good fruit;
or men of corrupt minds deliver good and sound doctrine, or the wholesome words of our Lord Jesus Christ: but here they seem to be applicable to other persons, even true believers and hypocrites: the former are comparable to good trees, and are called trees of righteousness, which being planted by the river of the love of God, and rooted in Christ, and filled with the fruits of righteousness by him, do not bring forth the evil fruit of sin, as the common and constant course of their lives and conversations; for that they never commit sin, or are entirely without it, cannot be said; but sin is not their usual and common practice, or they do not live in sin: and the latter, hypocrites, who pretend to a great deal of religion, and have none that is true and real, these are comparable to corrupt trees; which, though they may make a fair show, yet do not bring forth good fruit, or perform works of righteousness which are truly such; what they do have only the appearance of good works, and are not properly so;

(See Gill on Matthew 7:16). (See Gill on Matthew 7:17). (See Gill on Matthew 7:18).