Repentance
God lives in holiness and men cannot see Him. Sin has built a wall between God and men. Jesus delivers us from sin. Men have to repent of their sins. Repentance means asking God for forgiveness in the name of Jesus Christ, turning away from sin and not sinning again. -> How does Jesus deliver us from sin? The parable of the new wine shows the importance of repentance. In the past, wine was held in wineskins*. The old wineskin cannot be filled with new wine as it might burst. In the same way, men cannot receive the Holy Spirit. If they believe in Jesus and repent of their sin(s), (sin inhabits men, men are bad) and get water baptised, they are like a new wineskin that can be filled with new wine without bursting:
"Nor do they put new wine into old wineskins, or else the wineskins break, the wine is spilled, and the wineskins are ruined. But they put new wine into new wineskins, and both are preserved." (Matthew 9:17, NKJV)
Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit. For the promise is to you and to your children, and to all who are afar off, as many as the Lord our God will call." (Acts 2:38-39, NKJV)
*Wineskin: the skin of a sheep or goat sewn up and used as a holder for wine (Collins).