Ephesians 4:18-19

They are darkened in their understanding and separated from the life of God because of the ignorance that is in them due to the hardening of their hearts.

(v18, NIV)

So we are not to walk as the Gentiles do. How do the Gentiles walk and why are they the way that they are? Well, they do not walk in the truth for they are not followers of the Lord Jesus Christ. They simply do not understand or do not know the truth and life that is found in Christ Jesus. This is because their hearts have been hardened. They dare not open up their hearts to the welcoming love that is found in our Lord and savior. Pharaoh's heart was also hardened when Moses asked to let his people go. God sent plague after plague upon the Egyptians, but due to Pharaoh's hardened heart, he would not let the Israelites go.

Having lost all sensitivity, they have given themselves over to sensuality so as to indulge in every kind of impurity, with a continual lust for more.

(v19, NIV)

Playing guitar is one way in which you can develop calluses. It may hurt at first, but after a while, your finger tips become hard and your fingers don't hurt as much anymore when playing the guitar. Calluses can develop doing something other than playing guitar. Sometimes people will wear gloves when living weights because if they do not, they may develop calluses on their hands. This may also apply to batting in baseball or playing golf. The gloves protect their hands from the pain they may feel at first when doing whatever they need to do. However, after bearing with the pain and keeping at it, calluses develop on your hands and you won't feel the pain as much anymore. In the same way, the Gentiles have become callous. When they first gave into sinfulness of the flesh, it was painful and quite shocking. However, if they kept at it and were bearing with the pain, they got used to it. Continuing to indulge in their sins resulted in them not necessarily feeling the same weight or pain or burden they initially felt from their sin. They started to accept it as it was and fell deeper and deeper into their sins. We are not to live as they do and we are not to develop calluses with regards to our sins and sinful nature. See sin for what it really is and do not learn to accept it and fall deeper into your sins.

The callusing I can see in the culture nowadays. In media and television and movies we can see how they become more perverse and cruder. If you compare the movies we see today with ones we saw 10 years ago, on average, they are much worse nowadays. The society is accepting more nudity, more sexuality, more cursing and more violence than before. A movie rated R 10 years ago would maybe only receive a PG-13 rating nowadays. Maybe I'm exaggerating, but I forgot the rating system and what comes between PG-13 and R. Regardless, do not become calloused and do not lose sensitivity. See sin for what it is and despise it. Live a life worthy of your calling.