testifies with our spirit that we are God’s children.(Romans 8:16)
6Because you are sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, "Abba,[a] Father."(Gal.4:6)
24Those who obey his commands live in him, and he in them. And this is how we know that he lives in us: We know it by the Spirit he gave us.( 1 John 3:24)
13We know that we live in him and he in us, because he has given us of his Spirit.( 1 John 4:13)
You and I cannot be saved apart from the Holy Spirit. In fact, Paul makes it clear how each member of the Holy Trinity is involved in your salvation. (W.Wiersbe)
As far as God the Father is concerned, I was saved when He chose me in Christ before the world and time began. As far as God the Son is concerned, I was saved when He died for me on the Cross.. As far as God the Holy Spirit is concerned, I was saved in July 1970, at the altar of Shepherd Gospel temple, when I responded to the preaching of the word, and recognized as a young man of ten that I needed my sins forgiven and asked Jesus to come into my life and be my Lord and Savior. I did not understand all the theology, but I could tell you with assurance, that I knew, that I knew, that I knew I was a child of God.
Not only are contagious believers infected by Jesus,
2. CONTAGIOUS BELIEVERS ARE INFECTIOUS FOR JESUS!(5-8)

A. Contagious believers become more like Christ.

Contagious believers are infected with Jesus, and the truth is, contagious believers are infectious—they have an impact on an unbelieving world. So, how do contagious believers infect others with the love of Jesus? Paul told the Thessalonian Christians that their impact on the world was due to the fact that they, “6became imitators of …the Lord.” That is, they became more like Christ every day. Contagious believers become more like Christ, and that is bound to impact the world.

Eugenia Price says, “If Christ lives in us, controlling our personalities, we will leave glorious marks on the lives we touch. Not because of us but because of him.”

The Thessalonians made a glorious mark on the world because Christ lived in them and controlled them. Billy Graham said, “Our greatest need today is not more Christianity but more true Christians. The world can argue against Christianity as an institution, but there is no convincing argument against a person who, through the Spirit of God, has been made Christlike.”

Contagious believers infect the world with God’s love because they are becoming more like Jesus.

B. Contagious believers experience deeper levels of joy because of the Holy Spirit.

Not only are contagious believers infectious because they are becoming more like Jesus, but they are contagious because they experience deeper levels of joy because the Holy Spirit is in their hearts.

Paul speaks with admiration and wonder about the Thessalonian believers: “…In spite of persecution,” Paul said, “ you received the word with joy inspired by the Holy Spirit.”