Boasting means talking proudly about what you can do, what you have done, or what makes you special. In the Bible, boasting sometimes has a more positive meaning. "To glory in" means someone celebrates or gives honor to something good.
Boasting in the Old Testament
In the Old Testament, "boasting" describes the ungodly. They rely on their resources, not on God (Psalms 52:1; 94:3–4). Enemies of Israel boasted of their victories and claimed the glory for themselves (Deuteronomy 32:27; Psalms 10:3; 35:26; 73:9; Isaiah 3:9). They boasted of their riches and wisdom (Psalm 49:6; Isaiah 19:11). The Lord says the rich and wise should "boast in this, that he understands and knows Me, that I am the LORD, who exercises loving devotion, justice and righteousness on the earth" (Jeremiah 9:24).
Boasting in the New Testament
Jesus told a story about a proud Pharisee boasting to God in prayer (Luke 18:10–14). Most of the New Testament usages of the word occur in the apostle Paul’s letters. Boasting about your own achievements is wrong. Instead, the Bible teaches that it is good to praise what God has done. (Romans 3:27–28; 2 Corinthians 10:17; Galatians 6:14). Avoid self-righteousness and bragging (Romans 1:30; 2:17, 23; Ephesians 2:9; 2 Timothy 3:2). Paul linked boasting to the self-confident attitude of some Jews who had kept the law. For Paul, the only legitimate boasting was to boast (rejoice) in the Lord (Romans 5:11). Romans 5:3, contrasts the rabbinic view of glorying in sufferings with Paul's. Paul believed his sufferings pointed to God's power and his hope for the future.
Unlike his opponents, Paul did not boast by comparing himself to others. Because Christ worked through him and God commended him, he could give glory to God (2 Corinthians 3:2–6; 10:18). Paul preferred to boast of his weakness and the Lord’s power and strength (2 Corinthians 12:5, 9).
The apostle did boast about a group of Christians (2 Corinthians 7:4, 14; 8:24; 9:2–3). But he meant to show confidence in them, not to brag. Paul did not like to boast but did so to defend against critics in the Corinthian church. He said that those who should have praised him had instead forced him to engage in "foolish" boasting (2 Corinthians 12:11).