but, as the One who called you is holy, you also are to be holy in all your conduct;1 Peter 1:15(HCSB)
As the children of God, we are commanded to be holy because God is holy. But God is perfect and we are not perfect, so some may consider this to be an impossible task. However, when Scripture calls us to perfection, we have to understand that this is only achievable in the power of the Holy Spirit. It is only achievable as we live and move and have our being in our new born-again life in Christ, and not as we live and move and have our being in our old, fallen nature in Adam.
When we are born into God's family, the Holy Spirit comes to take up permanent residence within our hearts, and He starts a sanctifying work within our new, born again life in Christ. We are to grow in grace so that in His power, we will be conformed into the likeness of Christ, but the Spirit will ONLY sanctify our new life in Christ and not our old original sin nature.
On those occasions that we submit to our old sin nature and pander to the lust of the flesh, the enticements of the world, and the accusations of the devil, the Holy Spirit can do no sanctifying work in our new nature in Christ. When we are living under the influence of the old sin nature, we can NEVER EVER be holy – even the good things that are done in the flesh are unholy in God's eyes.
But when, by faith, we submit to the leading and guiding of the Holy Spirit and allow Him to govern our new life in Christ, it means that we put to death those ungodly lusts. It means that we keep the old sin nature nailed to the Cross. It means that we allow the Holy Spirit to do a good work within our new life in Christ, which will grow in grace and become more and more conformed into the likeness of Christ.
Jesus lived a holy life and demonstrated how we too can live a holy life. Jesus lived His whole life in submission to the Holy Spirit. He was "set apart unto God." Let us similarly live our lives in submission to the Holy Spirit "set apart unto God," for the One that called us and saved us and is sanctifying us is holy – and as we submit to the Holy Spirit in our lives and function in the sphere of the spirit (our own human spirit), we will fulfil this command.
As we allow the Holy Spirit to govern our new life in Christ, we will also be holy in all our conduct and behaviour.
Holy Father, I want to be holy as You are holy. There are times that I quench and grieve Your Spirit, when I live in the sphere of my old sin nature. Please help me to put to death the lusts of the flesh so that I may live a life that pleases You. May I love to be holy and set apart to do Your good will in my life, and may I live to Your praise and glory. In Jesus' name, AMEN.