Wrong desires, thoughts and speech are not a benign cultural difference, like a regional accent; they reveal a heart that is set against God being at the centre of that person's life.  They are not only an expression of self-assertion against the sufficiency of God's provision, they practically defy the rule of God; and give that right away to another.  The Bible name for an idea, thing or person that takes God's place is: an 'idol'.

The Old Testament is full of examples of God's wrath against idols and those who worship them (Psalm 135:15-18).  Today, many of our idols are found in the greedy lust for people or possessions – as well as in the ritual worship of natural things (paganism) or false deities, or false ideas about God.  But whatever the flavour of false worship, this verse tells us that those who indulge in it have no place in God's Kingdom (Galatians 5:21).  It is as serious as the warning is stark.

This may not sit well with the compromising tolerance of our day, that values personal happiness more highly than letting God rule.  Neither is it acceptable to those who want to redefine human relationships, justify corrupt business practice or selfish lifestyle, and assume that God is content.  But it is essential information for those who profess faith in Christ and those who do not yet, if they are to be part of His eternal kingdom.  If personal and behavioural idolatry was really acceptable to God, there would be no need for anybody to be told the Gospel or urged to obey its call to repentance (2 Thessalonians 1:8-10).

However, this verse is directed first to the Christians.  It is a warning for those who have believed in Christ not to remain in, or be seduced back into, old ways.  It remains essential advice for new Christians who might have thought that they could merge their old lifestyle with the new - they must not, nor can we.  That is why we have to keep close to the Lord.  It is also good to have other believers around at work, with whom you can pray regularly and who can call you to account.