Why does becoming a believer change your desires?
Becoming a believer changes desires because the believer is no longer in the flesh under old Adam but in the Spirit, under His control. All things have passed away, and all things become new. These are two totally different worlds, so desires change accordingly.
Les explains that when you become a believer, your whole circle of friendships will probably change, and your whole desire begins to change. That is as it should be, because it is two different worlds, totally two different worlds. He clarifies this does not mean we get so heavenly minded that we are no earthly good; we still function, work, and plan. There is nothing wrong with accumulating wealth or providing for family, as long as it is in God's timetable and plan. The change is rooted in Romans 8:9: you are not in the flesh, not under old Adam, but in the Spirit, under His control instead of old Adam, if the Holy Spirit is dwelling in you. All things have passed away, and all things become new.
More Questions
Why do your friendships and desires change after you become a believer?
When you become a believer, your friendships and desires will probably change, and that is expected because believers and unbelievers live in two totally different worlds.