Discerning truth from error is a fundamental skill that Christians must seek to grow in over time. Much like the Bereans, who examined the Scriptures daily to see if Paul's teachings were true. (Acts 17:11)
Consider the analogy of a jeweler: how does he discern a true diamond from a fraud or an imitation? The jeweler could learn everything he could about every false diamond, but the more effective method would be to master his knowledge of a true diamond, making anything that deviates from the true specifications easy to point out.
The same goes for Christians: the more we know about what's true, the easier it will be to spot what's false. Jesus says, "If you love me, you will keep my commandments.", which implies that we know what those commandments are. Seek to grow in your knowledge of God and his word, and you will be able to love him more fully and protect against error.
