We behave according to our desires.  If we want it, we will think about it, and plan how to get it ... then we take action.  So it matters greatly how we manage our desires and our thoughts.  Those whose minds are exposed to sinful ideas will start to desire them, and will find that they cannot stop sinning (James 1:13-15).

Reforming our mind and deep desires is an essential part of Christian discipleship (Romans 12:1-2).  Whatever we see and hear, and experience - if it pleases our sinful nature – will stoke the fires of desire which are already smouldering in our hearts.  To allow those flames to take hold is hellish, which is why we need to walk closely with the Lord to strengthen the holy desires He puts within us.  

On the other hand, those who are hungry to be like Jesus will give space for the Holy Spirit to work inside them - to give them the desire and the power to live like Christ (Philippians 2:13).  Play acting (hypocrisy) can successfully fool people about our holiness, but in the end, the true desire of the heart will be seen because its nature will inevitably be expressed (Luke 12:1-3).

Religion, based on rules with their threats and rewards, can never change somebody's heart.  Only God can.  When we repent and believe the gospel, God gives us His Spirit.  But if we choose to resist Him or persist in lusting after our own pleasure, we will also resist His work in changing us into the image of Christ.  Stop focussing on your external behaviour and look at your inner desires to see if they please the Lord (Ephesians 5:10), and then yearn to be like that.  As you do, the Spirit will enable you.