John Gill Commentary Ezekiel 3:21

"Nevertheless if thou warn the righteous man, that the righteous sin not, and he doth not sin, he shall surely live, because he took warning; and thou hast delivered thy soul." — Ezekiel 3:21 (ASV)

Nevertheless, if you warn the righteous [man]
Every righteous man, that is so in a judgment of charity, whether truly righteous or not, which the event shows; who should be warned not to trust in their own righteousness, but to depend on the righteousness of Christ; that they be careful to maintain good works, to avoid sin, and live holy lives and conversations, as follows:

that the righteous sin not ;
not that there is any just man that does good, and sins not; the best of men are often sinning in thought, word, or deed; but he is to be warned that he does not continue in sin, and lead a sinful course of life; which is contrary to his character, and to his faith in Christ for righteousness, which is attended with good works:

and he does not sin ;
the warning and exhortation given him having so good an effect, through the power of divine grace, as to be a means of preserving him from a vain conversation:

he shall surely live ;
spiritually and comfortably now, and eternally hereafter:

because he is warned ;
that being a means, and with the divine blessing taking effect:

also you have delivered your soul; (See Gill on Ezekiel 3:19).