Answer: God's people must live self-controlled, upright and godly lives, being purified by Christ, and eager to do what is good, (verses 12, 13, and 14).
MORE INFORMATION AND/OR OTHER SCRIPTURE REFERENCES:
The word translated "teaches," as in "the grace of God teaches us to live self-controlled, upright and godly lives," refers to more than instruction; it includes the whole process of training a child--instruction, encouragement, correction and discipline. We are never left in doubt as to what self-controlled, upright and godly lives are. We must always strive to mature in all areas that produce godly lives/godly actions and good works, which pleases our Father, and which is a result of wearing His righteousness--being clothed with Christ:
Isaiah 61:10: "I delight greatly in the Lord; my soul rejoices in my God. For He has clothed me with garments of salvation and arrayed me in a robe of righteousness, as a bridegroom adorns his head like a priest, and as a bride adorns herself with her jewels."
Galatians 3:26-27: "You are all sons of God through faith in Christ Jesus, for all of you who were baptized into Christ have clothed yourselves with Christ."
The striving for the maturity to lead self-controlled, upright and godly lives is an ongoing process, and Christ says that it is done "in keeping with repentance."
If we truly had a godly repentance when we were led to Christ and converted, then we will live that repentance--a changed life, as "repentance" means "to change one's mind or purpose, involving a change for the better, an amendment," as should happen when we repent of our sins. This is usually stated, "to be sorry, and change."
Matthew 3:8: [Jesus said,] "Produce fruit in keeping with repentance."
Jesus says that we will be recognized as true or false by our fruits:
Matthew 7:17-20: "Likewise every good tree bears good fruit, but a bad tree bears bad fruit. A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Thus, by their fruit you will recognize them."
Self-Control: Having every attitude, characteristic, appetite, desire, thought, etc., under control of reason, and all reason itself under the control of God through the Holy Spirit, Who lives in God's children. This simply means that every area of a Christian's life is guided by the Word of God:
Proverbs 25:28: "Like a city whose walls are broken down is a man who lacks self-control."
Galatians 5:22-25: "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law. Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. Since we live by the Spirit, let us keep in step with the Spirit."
2 Timothy 3:1-5: "But mark this: There will be terrible times in the last days. People will be lovers of themselves, lovers of money, boastful, proud, abusive, disobedient to their parents, ungrateful, unholy, without love, unforgiving, slanderous, without self-control, brutal, not lovers of the good, treacherous, rash, conceited, lovers of pleasure rather than lovers of God--having a form of godliness but denying its power. Have nothing to do with them."
2 Peter 1:5-9: "For this very reason, make every effort to add to your faith goodness; and to goodness, knowledge; and to knowledge, self-control; and to self-control, perseverance; and to perseverance, godliness; and to godliness, brotherly kindness; and to brotherly kindness, love. For if you possess these qualities in increasing measure, they will keep you from being ineffective and unproductive in your knowledge of our Lord Jesus Christ. But if anyone does not have them, he is nearsighted and blind, and has forgotten that he has been cleansed from his past sins."
Upright: To "live an upright life" is to life righteously. To live righteously is the consequence of being made righteous. Since "there is no one righteous, no not one" (Romans 3:10), God imputes, or credits, to the believer the perfect righteousness, both active and passive, of His Representative and Surety, Jesus Christ, (Romans 10:3-9). Justification (to be made righteous or upright in the sight of God) is not the forgiveness of a man without righteousness, but a declaration that he possesses righteousness, which perfectly and forever satisfies the law, namely, Christ's righteousness:
2 Corinthians 5:21: "God made Him Who had no sin to be sin for us, so that in Him we might become the righteousness of God."
Romans 4:6-8: "David says the same thing when he speaks of the blessedness of the man to whom God credits righteousness apart from works: ‘Blessed are they whose transgressions are forgiven, whose sins are covered. Blessed is the man whose sin the Lord will never count against him.'" [David is quoted here from Psalm 32:2.]
Living an upright, or righteous, life is NOT the basis for the child of God being justified (being made righteous); it is a consequence of being made righteous. A Christian must live as that new person who wears God's righteousness--who has become God's workmanship--and do those things which God has prepared for His righteous ones to do. Anyone claiming to be a Christian--claiming to wear the righteousness that only God can give--must live as one brought from death to life and live for God in Christ Jesus:
Ephesians 2:8-10: "For it is by grace you have been saved, through faith--and this not from yourselves, it is the gift of God--not by works, so that no one can boast. For we are God's workmanship, created in Christ Jesus to do good works, which God prepared in advance for us to do."
Romans 6:8-14: "Now if we died with Christ, we believe that we will also live with Him. For we know that since Christ was raised from the dead, He cannot die again; death no longer has mastery over Him. The death He died, He died to sin once for all; but the life He lives, He lives to God. In the same way, count yourselves dead to sin but alive to God in Christ Jesus. Therefore do not let sin reign in your mortal body so that you obey its evil desires. Do not offer the parts of your body to sin, as instruments of wickedness, but rather offer yourselves to God, as those who have been brought from death to life; and offer the parts of your body to Him as instruments of righteousness. For sin shall not be your master, because you are not under law, but under grace."
Romans 6:19-23: "I put this in human terms because you are weak in your natural selves. Just as you used to offer the parts of your body in slavery to impurity and to ever-increasing wickedness, so now offer them in slavery to righteousness leading to holiness. When you were slaves to sin, you were free from the control of righteousness. What benefit did you reap at that time from the things you are now ashamed of? Those things result in death! But now that you have been set free from sin and have become slaves to God, the benefit you reap leads to holiness [Hebrews 10:14: "because by one sacrifice He has made perfect forever those who are being made holy."], and the result is eternal life. For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord."
Romans 7:4-6: "So, my brothers, you also died to the law through the body of Christ, that you might belong to another, to Him Who was raised from the dead, in order that we might bear fruit to God. For when we were controlled by the sinful nature, the sinful passions aroused by the law were at work in our bodies, so that we bore fruit for death. But now, by dying to what once bound us, we have been released from the law so that we serve in the new way of the Spirit, and not in the old way of the written code."
All of these things are done because we have been purified by Christ, and no one who lives in Him (and thus, in God) deliberately keeps on sinning, or participating in and a slave to the world of darkness:
1 Peter 1:22-23: "Now that you have purified yourselves by obeying the Truth so that you have sincere love for your brothers, love one another deeply, from the heart. For you have been born again, not of perishable seed, but of imperishable, through the living and enduring Word of God."
1 John 3:1-6: "How great is the love the Father has lavished on us, that we should be called children of God! And that is what we are! The reason the world does not know us is that it did not know Him. Dear friends, now we are children of God, and what we will be has not yet been made known. But we know that when He appears, we shall be like Him, for we shall see Him as He is. Everyone who has this hope in him purifies himself, just as He is pure. Everyone who sins breaks the law; in fact, sin is lawlessness. But you know that He appeared so that He might take away our sins. And in Him is no sin. No one who lives in Him keeps on sinning. No one who continues to sin has either seen Him or known Him."
Some results of living a self-controlled, upright and godly life--of living a life that shows forth the righteousness with which He has covered us--to the glory of the Father, and why we should do so:
Isaiah 32:17: "The fruit of righteousness will be peace; the effect of righteousness will be quietness and confidence forever."
Galatians 5:22-26: "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law. Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. Since we live by the Spirit, let us keep in step with the Spirit. Let us not become conceited, provoking and envying each other."
Ephesians 5:8-10: "For you were once darkness, but now you are light in the Lord. Live as children of light (for the fruit of the light consists in all goodness, righteousness and Truth) and find out what pleases the Lord."
Colossians 1:9-14: "For this reason, since the day we heard about you, we have not stopped praying for you and asking God to fill you with the knowledge of His Will through all spiritual wisdom and understanding. And we pray this in order that you may live a life worthy of the Lord and may please Him in every way: bearing fruit in every good work, growing in the knowledge of God, being strengthened with all power according to His glorious might so that you may have great endurance and patience, and joyfully giving thanks to the Father, Who has qualified you to share in the inheritance of the saints in the kingdom of light. For He has rescued us from the dominion of darkness and brought us into the kingdom of the Son He loves, in Whom we have redemption, the forgiveness of sins."
