If one were to do a bit of reading, he would see that many who have historically asked the first titled question really intend to answer, “Was the Holy Spirit active in an Old Testament believer’s salvation and sanctification?” And, because most would at least say that the Spirit was active at the initial point of a believer’s salvation in the OT (cf. Deut 30:6 with Rom 2:29), usually the intention is to discover the similarity or disparity between how believers are progressively sanctified from one testament to the next.
In the OT, the Spirit of God is said to occasionally or even continuously empower some of those who ruled over Israel (e.g., Num 11:17, 25; 1 Sam 11:6; 16:13). On rarer occasion, the Spirit also granted unique skills and strength to individuals to aid Israel in some way (e.g., Ex 31:3; 35:31; Judg 15:4). These works of the Spirit are not necessarily transformational in the sense that the individual so empowered was being progressively sanctified through these unique works of the Spirit. At the same time, an individual’s lack of sanctified behavior could forfeit one of these unique works of the Spirit (1 Sam 16:14; cf. Judg 16:20).
So, if we are looking at any of the above works to answer the question, “Did the Holy Spirit dwell in Old Testament believers,” assumedly as He does NT believers (something continuous and part-and-parcel of our salvation and sanctification; cf. Rom 8:9–11), we don’t have enough biblical data from the above to answer our question. And, if our true intention is to really answer the question, “Was the Holy Spirit active in an Old Testament Believer’s salvation and sanctification,” the passages cited above are not directly to the point. The above works of the Spirit are not necessarily intended for an individual’s sanctification but for unique works of service that benefit others in some way, perhaps somewhat analogous to the Spirit’s work in granting spiritual gifts today (again, please note the “somewhat”―the parallels are not perfect).
It would seem that Israel at some point and at least to some degree understood the nature of the Spirit’s indwelling when God promised as much to the nation through some of her prophets (Ezek 11:19–20; 36:26–27; 37:14; cf. Jer 31:31–34). And while good men beg to differ, it is my understanding that what was promised involves the scope of this indwelling (for all of Israel) and not so much that God would sanctify the recipients of these promises in a fundamentally different way than how He had been doing so for individual believers in any OT era (i.e., that He would be in them and not just near them with His presence in Israel’s temple or in some other way). If this understanding is correct, one is then left to figure out whether or not what was promised to all of Israel was already true of believing Israelites in the OT (or other believers that lived before Israel came to be, for that matter).
My painfully short answer to that final question is this―if one can be told that God created all things in the OT and then find out in the progress of revelation that the Son was involved in this creation (see Gen 1:1 with Col 1:16), so also we could be told in the OT, for example, that some walked with God (e.g., Gen 5:21; 6:9) and can now describe this walk in NT terms, that is, that the Spirit was at work in their sanctification. The absence of this terminology in the OT does not necessarily mean that this work of the Spirit was absent at that time as well. And to say that selective, occasional empowerments in the OT prove that progressive sanctification by the Spirit for all OT believers was missing would be akin to talking only about spiritual gifts in the NT when asking how sanctification works today. What is difficult is that the matter is not later detailed as, say, something like Christ’s involvement in creation. And for this reason, we should show each other charity when we do not theologically connect the dots of biblical data on this matter in the same way.
To put it another way, one can say that the Spirit was active in salvation and sanctification in the OT and still recognize that there are differences between the Spirit’s manifold work in the OT and NT believers today, such as unique empowerments for service. The Spirit’s selective and occasional works for service then are now matched by a uniform grace to all believers to serve the body of Christ, recognizing that this grace is variously tailored for and thus differently displayed by one Christian to the next (1 Cor 12; 1 Pet 4:10–11). For those such as myself, the difference for the Spirit’s work in a believer from one testament to the next primarily involves what is given (or not) for his service and not for his sanctification and certainly not for his salvation.
A final caveat would be this―if the Spirit’s grace for unique works of service was selective and infrequent in the OT, and if the Spirit’s grace for gifts in the NT is universal (though varied in manifestation), and if this grace is intended for building up our fellow Christian (1 Cor 12:7), then we certainly enjoy a regular means of grace that aids our sanctification in a way that was not enjoyed before Pentecost. Yet still, to say that we have an external aid today that believers did not have then still falls short of saying that there is a fundamental difference between the Spirit’s internal work in sanctification from one testament to the next.