Yes, Christians do sin. The great Apostle Paul struggled with personal sin. Romans 7:15, 17-25 (ESV), 15 “For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate. … 17 So now it is no longer I who do it, but sin that dwells within me. 18 For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. 19 For I do not do the good I want, but the evil I do not want is what I keep on doing. 20 Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me…For I delight in the law of God, in my inner being, 23 but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. 24 Wretched man that I am! Who will deliver me from this body of death? 25 Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.”

What should we do when we sin? We need to confess our sins to God and ask Him to forgive us through Jesus’s blood. “If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.” 1 John 1:9 (ESV). The Greek word for unrighteousness has the thought of willfulness. The aspect of a sin that is partially willful needs to be cleansed through hard experiences. (See 2 Corinthians 7:11.)

We should certainly strive against sin as the struggle teaches us where and how we need to change. We learn about our secret and open faults. Psalm 19:9, 11-12 (NKJV), 9 “…The judgments of the LORD are true and righteous altogether. … 11 Moreover by them Your servant is warned, and in keeping them there is great reward. 12 Who can understand his errors? Cleanse me from secret faults.” 

Finally, we must remain very humble and not become prideful by our progress. As the Apostle Paul wrote, “Therefore let anyone who thinks that he stands take heed lest he fall.” 1 Corinthians 10:12 (ESV). We do not want to become puffed up with pride, thinking we are perfect now.

Additional Resources: 
Christian Questions Podcast 
Episode #1243: “Am I Putting New Wine in an Old Wineskin?” 
Three parables to help us stretch with the Christian development required of us  
Preview Video  
CQ Rewind Show Notes

Episode #1082: “How Do I Live a Life of Repentance?”
Learning what repentance is and is not and how it changes lives
Preview Video
CQ Rewind Show Notes

For children, parents and Bible Class teachers:
Animated video: “Why should we forgive others?”