Christians have a duty to stay grounded in the Word of God. We must actively live in the truth in order to be able to point out falsehoods and false prophets when they come our way. Jesus warns us in Matthew 7:15-23 against such things, saying that false prophets will come to us in the “sheep’s clothing, but inwardly are ravenous” (v.15). In other words, they appear to be trustworthy on the outside but on the inside, they are full of lies and deceit and are actively trying to lead people into the kingdom of darkness.
We have a way to discern and identify these types of teachers, though. Jesus tells us that we “will know them by their fruits (v.16). We can know whether they are from God or not by how they live their lives, and what the content of their message contains. Namely, do they teach salvation and assurance in Christ alone, or something else? If they teach assurance in Christ alone, they are not false and should be listened to. But if they teach assurance in anything else, we should run from them and have nothing to do with them.
Finally, Jesus gives a practical view of what false teachers can look like (v.21-23). They are people who often do the right deeds, even believe the right things, but they have no delight in Christ. Their life revolves around themselves, not Jesus. Even the good deeds they do are not done with the right motives. We are given hope, though, and a correct way to live. We must “do the will of [the] Father who is in heaven (v.21). Meaning, we must return daily to the cross to repent of our sins and place our faith in Jesus, and be people of the Word so that we are not lead astray by any false teaching; staying wholly and entirely focused on Christ alone for our salvation.