In 1 Thessalonians 5:23-24, Paul prays that God might sanctify the Thessalonian church completely. If there is one prayer that the church should pray with great frequency, it is this one. In a few short words Paul is telling this church that his complete confidence in their salvation and ongoing growth in Christian maturity and holiness is in God alone. Not only that, Paul's confidence in God's work in the life of believers is so strong that he writes, "He will surely do it."
We should be careful to note that these comments from Paul follow a list of instructions for this church to live and grow as God's people having peace among themselves. They have been instructed to be long-suffering with each other, have a community wide God-directed focus, and to never despise good instruction from God's word.
When Paul then tells this church that it is God who will sanctify them completely and that he will surely do it, he is not encouraging them to passivity in the faith.
Consider what Paul later writes to the church in Philippi. Philippians 2:12-13 Therefore, my beloved, as you have always obeyed, so now, not only as in my presence but 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 work for his good pleasure. There are two very important truths in these verses.
1. God does not save us to be passive in faith.
In Philippians 2:12, Paul refers to the time that he was with the Philippian church. This church has obviously come to faith in Jesus Christ and had obeyed the call of the gospel. While Paul was with them, he saw their immediate obedience to the truth of Christ in the transformation of their lives. He therefore wants to encourage this church to be this way even more while he, the Apostle, is not with them. They need to continue to rely on Christ in their Christian life, not the Apostle. He therefore gives them an instruction for his absence. "Work out your salvation with fear and trembling." In other words, Paul is telling them to continue in obedience in the faith even in his absence because their faith is lived before the exalted Christ who is King and God.
2. It is God who works out our salvation for his glory.
In Philippians 2:13, Paul makes a very comforting statement. As we live by faith before the Lord, the Lord is working that faith out in our life as he grows us to be more like him. He is doing the work in us. Look again at Paul's words: "for it is God who works in you." The God of the universe who works all things to his glory is working in believers to reflect his holiness. God is doing it for his pleasure and God is perfectly pleased in his own perfect character. If God is doing a work in us that pleases him, it means that this work will end in us being a perfect reflection of his own goodness. Will God fail? No, he is God.
We do not become holy because we can manufacture our own holiness. We become holy because God is holy, and he has saved us to be his children. God is working HIS holiness in us as we live by faith in him. His holiness will grow in us as he works in us and as his ultimate purpose is to bring everything to its perfect completion.
Do you ever wonder if the life ahead for you as a Christian is one that matures in the holiness of your Savior? Trust in Christ. Obey his word. Believe his truth. Apply his wisdom. Enjoy his grace. Hold onto his mercy. Look at his beauty. Live in his hope.
And in this application of faith, watch him work!