The Apostle, St.Paul, explains, “I beat my body and make it my slave so that after I have preached to others, I myself will not be disqualified for the prize” (1 Cor 9:27). Here the prize is salvation, as is clear from the preceding verses. Saint Paul follows a disciplined life because he knows that there is a possibility that he might forfeit the salvation that he preaches. For this reason, in the very next chapter, Paul encourages the Christians in Corinth to do the same: “So, if you think you are standing firm, be careful that you don’t fall” (1 Cor 10:12). The “fall” here is the “fall from grace” spoken about by Paul in Galatians 5:4. Interestingly enough, the warning about falling from grace in Galatians 5:4 is immediately followed up by Paul’s exhortation to have “faith working through love” in Galatians 5:6.
Since the Apostle believes that one might fall from grace, he elsewhere encourages the Christians in Philippi to “work out your salvation with fear and trembling” (Phil 2:12). Here again we see Paul’s emphasis on a “faith working through love” (Gal 5:6). We are to work out our salvation. While it is a gift, it requires our effort. If you receive the gift of a bicycle, it is worthless until you actually get on the bike and start peddling. If the giver of the gift saw the bicycle leaning against the wall in your garage covered in dust, he would be offended. The giver wanted the recipient to enjoy cycling, but this intention was never realized. The same is true of salvation. The gift of salvation has been given to us so that we can be conformed to the image of His Son (Rom 8:29). This is a profound honor. We are called not only to believe in Christ, but also to become like Christ. We participate in the life of Christ. It is for this reason that we are called Christians. This means that our life is characterized by acts pertaining to faith, hope, and charity (1 Cor 13:13). When we willingly break the bond our bond of charity with Christ, we fall from grace.
from: pauliscatholic.com