As glorious as the accomplishment of the redemption of Christ is the gospel would not be “good news” if we had to do something to merit or achieve it. Like a skinny, boney-kneed, white kid trying to dunk a basketball we would just never get high-enough. Potential salvation is a mission-impossible salvation because it depends on weak, helpless sinners. But this is not the case. Just as God worked personally and powerfully in the accomplishment of redemption so too he works personally and powerfully in the application of redemption.
And because you are sons, God has sent the Spirit of his Son into our hearts, crying, “Abba! Father!” 7 So you are no longer a slave, but a son, and if a son, then an heir through God. (Gal. 4:6-7)
Just as the Father sent the Son into the world (Gal. 4:4) so he sends the Holy Spirit into the world. More specifically, he sends the Holy Spirit to those who were slaves and makes them sons.
In this way God calls (Rom. 8:30) us out of darkness (1 Pet. 2:9) into his kingdom and glory for fellowship with Jesus (1 Cor. 1:9; 1 Thes. 2:12; Col. 1:12-13). We who were formerly enemies (Rom. 5:10) and dead in our sins (Eph. 2:1-3) are made alive (Eph. 2:4) and caused to be born again by God (1 Pet. 1:3). The Holy Spirit graciously makes us to see the infinite value and supremacy of Christ (2 Cor. 4:4-6). He grants us repentance that leads to life (Acts 11:18) and faith to trust in Jesus (Eph. 2:8-10) as children adopted by God into his family (Eph. 1:5; Gal. 4:4-7). Furthermore, this application is not something that wears out. God the Holy Spirit continues to keep, guard, and persevere his people until we are ultimately presented holy, blameless and beyond reproach before God (1:22). In other words, God—who began the work, is willing and able and committed to finish it (Phil. 1:6; Rom. 8:28-30)!
This is of tremendous personal encouragement.
 Full-disclosure: I am the skinny, boney-kneed, white kid in this illustration.