12 Therefore, my beloved, as you have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling;
13 for it is God who works in you both to will and to do for His good pleasure.
Our obedience to God is how we work not for, but work out the salvation we have been given. As we choose to yield and be obedient to God’s Word, He empowers us to obtain our victory over the world in which we live, for the word salvation means to be delivered. We are in the world but not of this world. This is the victory that overcomes the world, our faith. Faith is obedience to God’s Word.
Smith Wigglesworth used to say faith is an act. If you go to Hebrews chapter eleven known as the hall of faith, you will find that all these people who were spoken of by God as having faith simply did what God told them to do. For example Noah was told to build an ark, so Noah built an ark. Abraham was told to leave his family and go out into the wilderness, and so he did etc.
Jesus has already purchased all we need through His shed blood which is found in the salvation He has given us, but we must by faith work out that salvation. When you walk by faith it is God who is at work in you to do that which is pleasing unto Him. As you walk by faith, walking out what His Word teaches, His Word is at work accomplishing in and through you all He has provided through salvation.