From Anstey’s Doctrinal Definitions:
This is an aspect of the indwelling of the Holy Spirit—which the believer receives when He believes the gospel—that gives him the power to walk in the path of faith and the capability of discerning truth from error (2 Cor. 1:21; 1 John 2:20, 27).
The indwelling of the Spirit is an exclusively Christian blessing. Old Testament saints had the Spirit come upon them to perform special acts of God, but the Spirit of God did not reside in them as He does with Christians. In fact, Christians have the Spirit’s presence in both ways (John 14:16; Acts 2:1-4). The difference may be illustrated in a motor-boat and a sail-boat. One has its source of power from within and the other gets its power from the wind from without. The Old Testament saints are like the sailboat; they were “moved by the Holy Ghost [Spirit]” (2 Peter 1:21) when the Spirit came upon them. But like the blowing wind, this was intermittent. Those saved today in these Christian times have His divine presence within them at all times. Like the motor-boat, they are “led by the Spirit” (Rom. 8:14), and this is dependent on the believer’s surrender to the control of the Spirit who dwells within. This has to do with being “filled with the Spirit” (Eph. 5:18). (See Filled with the Spirit.)
The anointing of the Spirit of God was given to the Lord Jesus for the purpose of empowering His ministry. Scripture says, “God anointed Jesus of Nazareth with the Holy Ghost and with power: who went about doing good, and healing all that were oppressed of the devil” (Acts 4:27; 10:38; Heb. 1:9).