God is holy. He is perfect and blameless which is why sin cannot exist in His presence. In John 17:17, Jesus prays to God and asks Him to make His people holy by His truth. We cannot make ourselves holy; only God can do that.
Take a glass of water, for instance. If you wish to drink pure, clean water, you must do something to purify it like buying a filter. Then the filter will make the water pure for you to drink. We have to allow God to purify us so we will be holy. This process is called sanctification. After we receive Christ’s salvation, God begins this process of making us holy by teaching us how to think, treat others, and live as though we are redeemed.
This process is a process that is ongoing. That is the beautiful thing. God will never stop making us holy if we continually ask Him to and allow Him to be Lord of our lives. Spend some time in prayer today asking for God to be in charge of your life so you can see the amazing things He wants to do in your life.