Matthew 12:33 "Either make the tree good and its fruit good, or make the tree bad and its fruit bad, for the tree is known by its fruit. 34 You brood of vipers! How can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks. 35 The good person out of his good treasure brings forth good, and the evil person out of his evil treasure brings forth evil. 36 I tell you, on the day of judgment people will give account for every careless word they speak, 37 for by your words you will be justified, and by your words you will be condemned."
We can have a good orchard or a bad orchard depending upon how we care for the trees. The fruit of a well cared for orchard will be far better than one that is not cared for. Thus, we can make the tree good or make the tree bad. Likewise with people, good people bring forth good and evil people bring forth evil. Here's the problem with people, there are none that are good for the scriptures tell us only God is good (Matthew 19:17).
Among those Jesus was addressing were Scribes and Pharisees who believed they were good. Jesus called them a brood of vipers and He called the entire culture evil and adulterous (adulterous carried the idea of serving something other than the Lord). Jesus told the people that they could only speak out of the abundance of their heart, which Jeremiah the prophet called deceitfully wicked (Jeremiah 17:9). In Mark 7:21-22 and Matthew 15:18-19 Jesus reveals what is in the heart of people. It is not a dictionary we would want to choose our words from, yet Jesus tells us people speak out of the abundance of their hearts. Even more, He tells us that people will be judged for what they speak. Jesus says we will be justified by our words or condemned. All people should shudder at such a thought since all have evil hearts.
Jesus knowing all peoples' condition made a way to become good. He died on the cross, rose again from the dead on the third day and sat down at the right hand of God as Lord over all. He died on the cross to pay sin's penalty (Romans 5:10), to render sin powerless (Romans 6:6-7) and to render Satan powerless (Hebrews 2:14-15). All who repent of their sin and believe in Jesus receive forgiveness of sins and receive the Holy Spirit (Ephesians 1:13-14). All believers are in Christ and become new creatures in Christ (2 Corinthians 5:17). The believers become good in Christ, because God is good and will be justified at the final judgment. Believers confess with their mouth that Jesus is Lord and believe in their heart that God raised Him from the dead and are saved (Romans 10:9).
Believers in Jesus can bear good fruit because God is in charge of their lives. We bear good fruit by obeying the Lord by faith. We attempt to be and do what He says expecting Him to fulfill our act of faith with His power. Read John 15:1-8; Galatians 5:22-23, Galatians 2:20.
If you are a believer, you have the capacity to bear good fruit. If you are not a believer, you have no capacity to bear good fruit. We use our capacity to speak and do good by obeying the word of God by faith. All believers can obey the Lord and produce good fruit.