We must be holy:

• Because the voice of God in Scripture plainly commands it.
• Because this is the one grand end and purpose for which Christ came into the world.
• Because this is the only sound evidence that we have saving faith in our Lord Jesus Christ.
• Because this is the only proof that we love the Lord Jesus Christ in sincerity.
• Because this is the only sound evidence that we are true children of God.
• Because this is the most likely way to do good to others.
• Because our present comfort depends much upon it.
• Because without holiness on earth we shall never be prepared to enjoy heaven.

– J.C. Ryle in Holiness