Old catechisms asked, "Why did God make you?" The answer: "God made me to know him, to love him, and to serve him in this world and to be happy with him forever in the next." Here, in just 26 words, is the whole reason for our existence. Jesus answered the question even more briefly: "I came so that [you] might have life and have it more abundantly" (John 10:10). God’s plan for you is simple. Your loving Father wants to give you all good things—especially eternal life. Jesus died on the cross to save us all from sin and the eternal separation from God that sin causes (CCC 599–623). When he saves us, he makes us part of his Body, which is the Church (1 Cor. 12:27–30). We thus become united with him and with Christians everywhere (on earth, in heaven, in purgatory).
What You Must Do to Be Saved
Best of all, the promise of eternal life is a gift, freely offered to us by God (CCC 1727). Our initial forgiveness and justification are not things we "earn" (CCC 2010). Jesus is the mediator who bridged the gap of sin that separates us from God (1 Tim. 2:5); he bridged it by dying for us. He has chosen to make us partners in the plan of salvation (1 Cor. 3:9). The Catholic Church teaches what the apostles taught and what the Bible teaches: We are saved by grace alone, but not by faith alone (which is what "Bible Christians" teach; see Jas. 2:24). When we come to God and are justified (that is, enter a right relationship with God), nothing preceding justification, whether faith or good works, earns grace. But then God plants his love in our hearts, and we should live out our faith by doing acts of love (Gal. 6:2).
Even though only God’s grace enables us to love others, these acts of love please him, and he promises to reward them with eternal life (Rom. 2:6–7, Gal. 6:6–10). Thus good works are meritorious. When we first come to God in faith, we have nothing in our hands to offer him. Then he gives us grace to obey his commandments in love, and he rewards us with salvation when we offer these acts of love back to him (Rom. 2:6–11, Gal. 6:6–10, Matt. 25:34–40).Jesus said it is not enough to have faith in him; we also must obey his commandments. "Why do you call me ‘Lord, Lord,’ but do not do the things I command?" (Luke 6:46, Matt. 7:21–23, 19:16–21). We do not "earn" our salvation through good works (Eph. 2:8–9, Rom. 9:16), but our faith in Christ puts us in a special grace-filled relationship with God so that our obedience and love, combined with our faith, will be rewarded with eternal life (Rom. 2:7, Gal. 6:8–9).
Paul said, "God is the one who, for his good purpose, works in you both to desire and to work" (Phil. 2:13). John explained that "the way we may be sure that we know him is to keep his commandments. Whoever says, ‘I know him,’ but does not keep his commandments is a liar, and the truth is not in him" (1 John 2:3–4, 3:19–24, 5:3–4). Since no gift can be forced on the recipient—gifts always can be rejected—even after we become justified, we can throw away the gift of salvation. We throw it away through grave (mortal) sin (John 15:5–6, Rom. 11:22–23, 1 Cor. 15:1–2; CCC 1854–1863). Paul tells us, "The wages of sin is death" (Rom. 6:23).
Read his letters and see how often Paul warned Christians against sin! He would not have felt compelled to do so if their sins could not exclude them from heaven (see, for example, 1 Cor. 6:9–10, Gal. 5:19–21). Paul reminded the Christians in Rome that God "will repay everyone according to his works: eternal life for those who seek glory, honor, and immortality through perseverance in good works, but wrath and fury to those who selfishly disobey the truth and obey wickedness" (Rom. 2:6–8).Sins are nothing but evil works (CCC 1849–1850). We can avoid sins by habitually performing good works. Every saint has known that the best way to keep free from sins is to embrace regular prayer, the sacraments (the Eucharist first of all), and charitable acts.