The “pure” that Paul is referring to in his letter to Titus are believers who have been saved by faith in Jesus and are sound in doctrine. These are the people who are pure and can rightly discern the good and evil. But, those who have rejected the truth of salvation by faith in Christ and who have replaced the teaching of the Word of Truth with “Jewish myths” or “human commands” (Titus 1:14) are still corrupt in sin, so to them everything remains impure.
“To those who are corrupted and do not believe, nothing is pure. In fact, both their minds and consciences are corrupted.” – Titus 1:15
Jesus said something similar in Matthew 15;10-11 and Mark 7:14-19 and Luke 11:37-41.
It appears the believers on the isle of Crete were focused on ceremonial practices and ritual
cleansing used to obtain favor, forgiveness and fellowship with God. None of these made any difference. These people had rejected the truth of the Word and salvation through Jesus Christ,
and instead had continued in purity observances which made no change in them. They remained corrupt and everything they did was corrupt.
Paul is not saying that there is nothing sinful for the Christian or that there are no morals that believers are expected to follow. Clearly there is evil and there is sin that must be avoided. But, ceremonial purity and ritual cleansing have zero impact on unbelievers to make them pure in God’s eyes and zero restoring value for the believer who is seeking restoration to fellowship with God.
If people are still trusting in rituals and ceremonies, then they really do not understand truth, they have no faith, and they have not been transformed. Thus, they are still corrupt. The believer who is pure should not allow these corrupt individuals define what constitutes the state of purity since
they themselves do not know.