In the context of the full counsel of scripture, although there are similarities between the Spirit’s work in the Old and New Testament, one glaring difference is the transient nature of the Spirit’s work prior to Christ’s incarnation. In the Old Testament, as described in this chapter, the Spirit of the Lord might come upon someone and then later depart from them. In the New Testament, as a result of Jesus’ work on the cross, we are sealed with the Holy Spirit and nothing can snatch us from Him or Him from us once we have committed our lives to Christ.
Nevertheless, we see at work in this chapter a principle that remains true today: a void must be filled. If you’ve filled your life with service to God, and then turn from that service, you will fill up that time with something. If you’ve filled your life with your children, and now they are grown, you will devote that time to something else, either with purpose or unintentionally. How much better it is to give thought to how to fill your time rather than to let the demands of the day, entertainment, or self-absorption fill those voids.
In Saul’s case, the void left by the departure of the Spirit of the Lord is filled by a harmful spirit. The text is clear that this spirit also is "from the Lord." That’s difficult for us to understand, but in the context of God’s desire to work all things together for good to those who love Him and are called according to His purpose, we can understand two things: First, for those called by God, there is no hell he won’t drag you through if that is what it takes to bring you back to Him. You may have heard the expression, “If you find yourself going through hell, whatever you do, don’t stop!” God knows our hearts and knows what it will take to turn us back from the destructive path we’ve chosen.
The second thing to bear in mind is that this promise is to those who love Him and are called according to His purpose. If we’ve rejected God, as Saul had, our hardships may not result in good for us, especially if we keep walking away from God.