THE SPIRIT IMPLIED
Both Epistles tell us that the church is composed of human beings, in this case, of Thessalonians. Thessalonica was an evil city, and for the most part those in that city were immoral people. Nevertheless, some who were once immoral were saved and regenerated and composed the church in their locality in the Triune God. For this reason, Paul speaks of the church of the Thessalonians in God the Father and the Lord Jesus Christ. By this expression Paul denotes the Triune God.
When some read concerning the church of the Thessalonians in the Triune God, they may say, “You claim that 1:1 indicates that the church is in the Triune God. Yes, this verse mentions the Father and the Lord Jesus Christ, the Son, but nothing is said concerning the Spirit. If this verse speaks of the Triune God, where is the Spirit?” Here we have one of the many instances where what the Bible does not say is just as important as what it does say, if not more so. Often in our contact with the saints, we may refrain from saying something to them. This may be more important than what we do say to them. Why did Paul not say “the church of the Thessalonians in God the Father, the Lord Jesus Christ, and the Holy Spirit”? Eventually we shall see that there is a good reason for Paul to mention the Father and Christ the Son, but not the Spirit.
Be assured that the very God spoken of in 1:1 is the Triune God. We know this by the fact that Paul first mentions the Father, the first of the Trinity. Whenever we have the first, we also have the second, the Son, and also the third, the Spirit. The very fact that Paul speaks of the Father is a strong indication that he is thinking of the Triune God. Moreover, the expression “the Lord Jesus Christ” implies the Spirit. The expressions “God the Father” and “the Lord Jesus Christ” both imply the Spirit. Therefore, in 1:1 the Spirit is implied and understood.
We must believe that the God referred to in 1:1 is the Triune God. To be in God the Father and the Lord Jesus Christ implies that we are also in the Spirit. Hence, in 1:1 we have the Triune God implied. This verse indicates that the church is in the Triune God.
IN THE TRIUNE GOD ORGANICALLY AND IN LIFE
It is a rather simple matter to say that the church is of God or of Christ. But it is deeper and more profound to declare that the church is in God the Father and in the Lord Jesus Christ. For example, it is one thing to say that we are of a particular person. However, it is altogether another matter to claim to be in that person. Humanly speaking, it is possible to be of someone, but it is not possible to be literally in that one. Only in a way that is organic and of life can the church be in the Triune God. We do not adequately understand the way of life, but God does understand it in full. Furthermore, only God can do something in the way of life. In a way that is organic and of life, God has made it possible for the church to be in the Triune God.
For the church to be merely of God, it is sufficient that God be merely our Creator. But for the church to be in God, God must become our Father, and we need to have a life relationship with Him. Likewise, for the church to be in the Lord Jesus Christ, Christ must be the Lord and Jesus to us.
VEILED BY TRADITIONAL CONCEPTS
Perhaps you have read 1:1 many times without realizing that the church is in the Triune God. Nevertheless, this fact is revealed in the Bible. Why is it, then, that not many Christians have seen it? The reason they do not see that the church is in the Triune God is that they are veiled by traditional concepts concerning the church. Believers may be familiar with expressions such as the church of God, the church of Christ, and the assembly of God, especially in the way they are employed today as denominational titles. But not many have realized that the church is in the Triune God.
It is important to realize that the New Testament does not say that the church is in God. First Thessalonians 1:1 tells us that the church is in God the Father and the Lord Jesus Christ. This is different from speaking of the church as merely in God, for it reveals that the church is in the Triune God. According to the Bible, there is no such thing as the church merely in God, but there is the church in the Triune God.
(Life-Study of 1 & 2 Thessalonians, Chapter 7, by Witness Lee)