In God the Father

The Thessalonians is the only epistle in which Paul addresses the assembly as "in God the Father." It was their characteristic feature. As little children, the Spirit of adoption filled them while they waited for God's Son from heaven (ch. 1:9, 10). And this, their blessed hope on which they dwelt much, worked into the very texture of their whole life here below. The coming of the Lord Jesus for His own was what they awaited, and by this Paul would see the fruit of his labor, as Paul's Master would also see the fruit of His labor (ch. 2:19).
To be established unblameable in holiness, and the time when holiness would have its true value, would be at that day (ch. 3:13). Those who had slept in Jesus would not lose the blessing of such a hope, and those who mourned their loss, for the moment, would see them again at that day (ch. 4:13-18). And lastly, God preserved His people to the time when Christ would come for them (ch. 5:23).
How heartily, then, could Paul give thanks about them, and always make mention of them in his prayers—not as though they needed something, but that they might be preserved in the freshness and true-heartedness of this beautiful condition of their Christian life. "Remembering without ceasing your work of faith, and labor of love, and patience of hope in our Lord Jesus Christ, in the sight of God and our Father.”