The Message of the Apostles
The apostles told people to repent as soon as they heard the true message of the kingdom of God, so they would not harden their hearts (Matt. 3:2; 4:17; Heb. 3:7-8).
What is this kingdom of God the apostles were telling people to enter? This kingdom of God is within your heart (Luke 17:21, KJV). God will give you a brand new heart so that you will want to obey Him, but you must be willing to change and allow Him to change you (Heb. 8:10).
You must maintain a child-like attitude to enter this kingdom (Matt. 18:3). You must have a "yes, Father, Your Will be done and not mine" attitude (Matt. 6:10). Instead of continuing to practice lawlessness, which simply means living the way that seems right to you, you agree to practice righteousness for God (Rom. 6:19; Prov. 14:12; 1 John 3:4, 7, 10). You agree to use the members of your body as instruments of righteousness (Rom. 6:13, 18-19).
Jesus died for your sins that you might live to righteousness (1 Peter 2:24). You live to righteousness by practicing righteousness, with the help of His Spirit, which He gives only to those who obey Him daily (1 John 2:29; Acts 5:32). You keep His sayings and do what He has commanded (Matt. 7:24; Luke 8:21; 11:28; John 8:51; 15:14). You glorify God by doing good works, which is your spiritual service of worship and what you were created in Christ Jesus to do (Rom. 12:1-2; Eph. 2:10).
Satan, who is the enemy of all righteousness, hates those who practice righteousness for God (Acts 13:10). Satan is against good works done for God's glory because he knows this is how his nature in you is crushed by God (Matt. 5:16; Rom. 16:20).
God's Will is righteousness (Heb. 13:21). Once you know the Will of God, you know the Way into the kingdom, which is true conversion (Matt. 7:21). You must be zealous and persevere as you overcome evil by doing good deeds for God (1 Peter 3:13; Luke 21:19; Rom. 12:21). You will be doing Jesus Christ's deeds as you strive to enter the narrow Way leading to the kingdom of God, which very few find (Rev. 2:26; Luke 13:24; 16:16; Matt. 7:14).
God's Ways are all good and you are to walk in them daily. Imitate the Way God lives and talks (Eph. 5:1; 1 Peter 4:11). Study God's word every day to find those things you can think, do and say to be pleasing in God's sight. The Lord will take notice and answer your prayers because you are living to please Him (1 John 3:22; John 9:31).
Once you start, you must endure (Heb. 10:36). Don't look back, but fight the good fight of faith (Luke 17:31-32; 9:62; 1 Tim. 6:12). It's easy (Matt. 11:30)! It's worth it! It is the very purpose of this life (Acts 5:20).