Updated: Jul 15, 2021
The work of the Holy Spirit, while not completely revealed in every instance, can be found in both the Old and New Testament writings. If one were to track the work of the Spirit of God in both Testaments, they would find His working in two main ways throughout the writings of scripture. Seeing these two ways can also help us view how God has chosen to work in the lives of His people.
Doing the Work and Will of God
First, we can see the work of the Spirit in enabling or compelling the people of God to do the work/will of God. While there are many examples of His working in this way, one of the clearest and easiest to spot is in the life of Sampson. The scripture speaks to the fact that Sampson would have specific times when the Spirit would come upon him compelling and empowering him to lead the people of God. (Judge 13:25) In the New Testament, we can see this same idea played out in the life of all believers, enabling their obedience toward God, confession of Christ, and love toward one another. Paul speaks to this specifically in his epistle to the Romans explaining to the believers at Rome, that it is His work in them and for them that guarantees the success of the work of God done through them. (Romans 8)
Speaking the Word of God
The second main way that we can view the working of the Holy Spirit, is related to the first. The Spirit can be found enabling or compelling the people of God to speak the words of God. This is seen in an obvious way in the inception of scripture (2 Pet. 1:21) but is also evident in God's people speaking about their God. Isaiah shows us this early in his writings. It was the Spirit that had anointed him to proclaim the good news (Isa 61:1–2) and comfort the people of God. A good New Testament example of this can be found in Luke 1:41, where we find for the first time, the Spirit not just coming upon, but filling Elizabeth and later her husband Zechariah, cause them both to prophesy. Like the believers in the New Testament and even into our day, it is the Spirit that causes and enables us to speak of the good news of Christ in love to those that are around us.
Overall, with each of these, the foundation of this work is in the regeneration of the heart of man. Although this is often veiled in the Old Testament, it is revealed in and display throughout the New Testament.
This clouded picture of the working of the Spirit can be seen in the belief of Abraham (Genesis 15:6), which is accounted to him as righteousness. The regenerating work of the Spirit can be the only explanation for the belief of Abraham, which was before any work on his part. This same Spirit regenerating work is not on full display and is revealed clearly to us in the Acts of the Apostles, and other New Testament writings.
 Malcolm B. Yarnell III, “The Person and Work of the Holy Spirit,” in A Theology for the Church, ed. Daniel L. Akin (Nashville: B&H Publishing Group, 2014), 483.  Ibid. 486.  Ibid. 494.  Ibid. 489.  Ibid. 494.  Ibid. 491.