The Spirit’s indwelling work can be seen in several places in the Old Testament besides the case of Joshua in Numbers 27:18. All of the Old Testament prophets are described as being indwelt by the Spirit as well as those who authored Scripture (2 Pet 1:19-21). Joseph in Genesis 41:38 is described as one “in whom is the Spirit of God” and Daniel in Daniel 4:8-9 is said to have the Holy Spirit from the perspective of the polytheistic worldview of the Babylonians. Bezalel is filled “with the Spirit of God” in Exodus 31:3 and given gifts of the Spirit in Exodus 35:30-36:1. I could give a description of every instance of an Old Testament believer having the Holy Spirit, but I will simply give you some of the biblical references: (Gen 41:38; Exo 31:3; 35:30-36; Num 11:17; 27:18; Deut 34:9; Judg 3:10; 6:34; 11:29; 13:25; 14:6, 19; 16:20; 1 Sam 10:6, 10; 11:6; 16:13-14; 19:20, 23; 1 Chron 12:18; 2 Chron 15:1; 20:14; 24:20; Neh 9:30; Psa 51:10-11; 139:7; 143:10; Isa 59:21; Eze 11:19-20; 36:25-27; 37:14; Dan 4:8-9; 5:11, 14).
You will notice that in many of these texts it says that the Holy Spirit “came upon them” and gave them special abilities (like Samson which he temporarily lost) or prophetic utterance. It is even used to refer to the Spirit working in unbelievers such as Balaam, King Saul, and Caiaphas (John 11:51) which can come and go. Therefore, this work of the Spirit is different than the saving indwelling work of the Spirit unique to believers. This “second blessing” is the giving of special gifts of the Spirit to individuals and is not a guarantee that they have the indwelling Spirit as a believer already. It also means that just as it cannot be proven that a person has a saving indwelling work of the Spirit just because the Spirit comes upon them, it cannot be proven that the Spirit coming upon them disproves the fact that they already have the indwelling work of the Spirit. This provides a further analogy to understand that the giving of the Spirit at Pentecost does not preclude a previous indwelling work if such a work is necessary for regeneration and sanctification without which no man can be saved (John 3:3; Heb 12:14).
Jesus says in John 3:3 that a man must be born again to be saved. But what does it mean to say that a man is born again if he is not indwelt by the Spirit? John 3:5’s “born of water” (which is essential to salvation) is an allusion to Ezekiel 36:25-27 which is a description of the cleansing and indwelling work of the Spirit. To be born again means to experience what Ezekiel 36:25-27 and Jeremiah 32:40 are talking about. If “normal” people could not be indwelt before Acts 2, how can Jesus say in Luke 11:13 that the Father will “give the Holy Spirit to those who ask him”? If Old Testament believers were not indwelt by the Holy Spirit, then could they be demon possessed? How can someone be regenerated or born again without the Holy Spirit indwelling them? How is sanctification possible without the indwelling work of the Holy Spirit? (1 Cor 2:10-16; 2 Cor 3:17-18). How can a person be adopted without the indwelling Spirit? (Rom 8:15; Gal 4:6-7). How can a person pray without the indwelling work of the Spirit? (Rom 8:26-27; Jude 1:20). Were Old Testament believers sealed by the Spirit? (Eph 1:13-14). How will they be raised from the dead? (Rom 8:11). How could they experience God’s love? (Rom 5:5). Were they among the worldly people who are “devoid of the Spirit”? (Jude 1:19). If they were devoid of the Spirit, why were they not worldly people?
The strongest argument in favor of all believers in all ages having the indwelling Spirit is that it is impossible to please God apart from him. Romans 8:7-9 says, “For the mind that is set on the flesh is hostile to God, for it does not submit to God’s law; indeed, it cannot. Those who are in the flesh cannot please God. You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him.” Were Old Testament believers in “the flesh” or in “the Spirit”? If they were in the flesh, then they could not be saved, since those in the flesh cannot please God, but faith and repentance are pleasing to him. How could they be in the Spirit or belong to Christ if they did not have the Spirit dwelling in them? Paul conditions being in the Spirit with the Spirit of God dwelling in them. For these reasons, the indwelling work of the Holy Spirit is necessary for all believers because man’s fallen condition has never changed after the fall.