The author is a cessationist who doesn't accept the charismatic teaching on the Holy Spirit, specifically, the baptism of the Holy Spirit. He doesn't actually come out and tell us this, but we are able to deduce it.
Jn. 3:5 Jesus answered, “I tell you the truth, no-one can enter the kingdom of God unless he is born of water and the Spirit. 6 Flesh gives birth to flesh, but the Spirit gives birth to spirit.
The indwelling Spirit is differentiated from the flesh:
Ro. 8:9 You, however, are controlled not by the sinful nature but by the Spirit, if the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, he does not belong to Christ.
We receive the Spirit by faith:
Ga. 3:2 I would like to learn just one thing from you: Did you receive the Spirit by observing the law, or by believing what you heard?
The baptism of the Holy Spirit is for everyone:
Lk. 3:16 John answered them all, “I baptize you with water. But one more powerful than I will come, the thongs of whose sandals I am not worthy to untie. He will baptize you with the Holy Spirit and with fire.
But we need to continually be refilled with the Holy Spirit:
Ep. 5:18 Do not get drunk on wine, which leads to debauchery. Instead, be filled with the Spirit.
Without the Holy Spirit, we are not saved. Without His continual refilling, we are nothing but carnal Christians.
We discuss the Holy Spirit baptism in some depth here.
----------------------