He has saved us and called us to a holy life—not because of anything we have done but because of his own purpose and grace. This grace was given us in Christ Jesus before the beginning of time. (2 Timothy 1:9 NIV)
God knows we are weak and frail human beings who are easily tempted by the things of this world. With the sacrifice of HIs only Son, Jesus Christ, God has made it possible for us to live our lives in a manner that is pleasing to Him through accepting Jesus as our Savior.
Although we are justified by our faith, as the Apostle Paul writes in his letter to the Romans, as believers we are to lead a holy life that demonstrates the love of God to others. The Holy Spirit, working within us, helps us to live a life that seeks holiness and avoids sin.
As believers, we can please God by striving to live holy lives because of the the grace He has given us.
“How does God save His people from the pleasure of sin? The answer is, ‘By imparting to them a nature which hates evil and loves holiness.’ This takes place when they are born again, so that actual salvation begins with regeneration. Of course it does; where else could it commence? Fallen man can neither perceive his desperate need of salvation, nor come to Christ for it, till he has been renewed by the Holy Spirit.” - A.W. Pink