What does it mean that you will know them by their fruit in Matthew 7:16?

TL;DR:

To “know them by their fruits” (Matthew 7:16 NKJV) means that deeds demonstrate what is in the heart. True believers’ deeds will show their love of Christ.

Matthew 7:16 uses the metaphor of bearing fruit to convey the good deeds that should be an outgrowth of faith. Fruit is used in this sense throughout the Bible. The Lord reads hearts (1 Samuel 16:7; Jeremiah 17:10), but people cannot, so deeds become evidence for what is in the heart. The Bible teaches that our deeds show our love for the Lord (Psalm 92:12–14; Matthew 7:16) and love for our neighbor (James 2:14–17; 1 John 3:16–18; 4:7–12). People can also bear bad fruit, their deeds revealing their unrighteous hearts. For example, when the Pharisees and Sadducees came to John the Baptist, he called them a "brood of vipers" and told them to "bear fruit in keeping with repentance" (Matthew 3:7–10). They were not to assume they were righteous because of their heritage or through ritual. They needed to be righteous in heart, which would be shown through their deeds. Jesus spoke a similar warning, saying, "How can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks" (Matthew 12:34; cf. Luke 6:43–45). Here and many other parts of the Bible teach that our actions are the outflow of the heart (Galatians 5:22–23). Our deeds demonstrate the truth of our words and our hearts.

from the old testament

In Jeremiah 17:10, the Lord expresses a connection between heart condition and deeds: “I the Lord search the heart and test the mind, to give every man according to his ways, according to the fruit of his deeds.” God searching the heart and giving “according to . . . the fruit of” one’s “deeds” implies that actions testify to what is in the heart.
Psalm 15:1–2 asks, “O LORD, who shall sojourn in your tent? Who shall dwell on your holy hill? He who walks blamelessly and does what is right and speaks truth in his heart.” This psalm implies that our deeds—our “walk” —affect our relationship with the Lord. Those who love the Lord should do “what is right.” In the subsequent verse, the psalmist gives examples of a blameless walk—e.g., not slandering or doing ill to one’s neighbor, not charging interest on loans, not taking bribes, and, of course, honoring God. The fruit of a good person shows in his actions.
Psalm 92:12–14 declares, "The righteous flourish like the palm tree and grow like a cedar in Lebanon. They are planted in the house of the LORD; they flourish in the courts of our God. They still bear fruit in old age; they are ever full of sap and green, to declare that the LORD is upright; he is my rock, and there is no unrighteousness in him." The faith of those who follow God is reflected in their actions, bearing fruit throughout their lives.

from the new testament

Matthew 7:16 says, “You will know them by their fruits. Do men gather grapes from thornbushes or figs from thistles?” (NKJV). In the verse before this, Jesus warned against “false prophets,” which is who “them” refers to. Jesus is saying that actions reveal what is in the heart—whether good or bad.
Galatians 5:22–23 describes the fruit of the Holy Spirit, explaining some characteristics of a person who lives by the Holy Spirit: "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law." When we see a life characterized by these things, we see the fruit of God's work.
Second Timothy 3:5 warns believers to stay away from those “having the appearance of godliness, but denying its power.” Anyone can call himself a Christian and attend church on Sundays, but the fruit that person yields will be the best indicator of true saving faith.
James 1:22 cautions believers, “But be doers of the word, and not hearers only, deceiving yourselves.” We are saved by grace, not works (Ephesians 2:8–9), but our actions give evidence of our faith (Ephesians 2:10).
James 2:14–17 also notes that kind words with no actions show a dead faith and a lack of true love for one’s neighbor.

implications for today

“Put your money where your mouth is.” “Walk the talk.” These common sayings express how important deeds are over just words. The Bible teaches this, too. Jesus noted that someone’s actions often reveal what is in that person’s heart (Matthew 7:16). How do your actions align with what you claim to be in your heart? When we open a box of cereal, we expect to find cereal, not sawdust. When we claim we’re Christian, our actions should show that we are Christ-like, not worldly. If we really believe God is who He says He is, our behavior should follow that belief. If we have received God’s love, we should be seeking to obey Him and seeking to love others (John 14:15; 15:1–17; 1 John 4:7–12; 5:1–5). If we are God’s child through faith in Christ (John 1:12), then we have the indwelling Holy Spirit at work in us transforming us to His image (Romans 8:28–30; Ephesians 1:13–14; Philippians 2:12–13). Christians aren’t perfect, but we should be aware of how our actions are a witness to others (1 John 1:8—2:6). What does the fruit of your life demonstrate about your relationship with Christ? What actions testify that Jesus is Lord of your life? Jesus’ words about knowing them by their fruit can also help Christians discern false teachers. Considering others’ deeds, not just their words, is wise. Our deeds demonstrate the truth of our words.

understand

Deeds reveal what is in the heart, whether good or bad.
True believers produce fruit that reflects their faith and relationship with God.
Actions provide clear evidence of genuine faith, distinguishing true believers from false ones.

reflect

How do your actions reflect the condition of your heart and your relationship with Christ?
What fruit in your life is evidence of your faith?
How do your daily choices either strengthen or hinder your witness for Christ?

engage

How can we encourage one another to bear good fruit that reflects our faith in Christ?
What are practical ways we can discern between genuine faith and false appearances in the people we follow?
How does the fruit of the Spirit manifest in the lives of believers, and how can we foster it?