What is biblical exegesis and what is biblical eisegesis and why is the latter so dangerous when reading and studying the Bible?
Eisegesis is, in short, the exact opposite of hermeneutics. Where hermeneutics is concerned with extracting the meaning out of biblical text, eisegesis (sometimes called “isogesis”) attempts to insert one’s own interpretation or meaning into the text. Concerns about eisegesis are that it uses human interpretation methods and human reasoning to reach conclusions about Scripture. You can see why eisegesis has created a lot of cults because they interpret the text in such a way as to introduce their own presuppositions, agendas or biases. That means their conclusions are subjective, rather than the objective truth found or extrapolated (hermeneutics) from the Word of God. What is subjective is subject to error, but what is objective truth cannot be wrong. At one Bible study the teacher asked, “What does this verse mean to you,” opening the door for eisegesis of the text. 
One problem is when only one text is used it takes the text out of the context the whole paragraph or chapter, so eisegesis is not recommended in any Bible study or private reading. Proof of that came when they went around the room to hear each person’s answer. There were as many answers as there were people in the room. We all know that Scripture has one meaning and one meaning alone, and it’s not for us to tamper with the meaning. Some use Mark 16:16 as proof that you must be baptized or you will not be saved, but that’s not what the verse actually says, so obviously, eisegesis is a dangerous practice for reading and studying Scripture because it can lead so many into error. To take a text out of context is to create a pretext, and likely a false one! Again, that’s where most of the cult came from and it’s easy to see why.
Hebrew, Greek, and Aramaic
The Old Testament was written in Hebrew, and unless you know Hebrew well enough, you’ll need a different translation of it, and indeed, there are hundreds. Some of the best when using all three of the languages in the Bible (Hebrew, Greek, and small portions of Aramaic) are the North American Standard Bible (NASB). This version does about the best job of them all when it comes to translating the original languages into the English language. The ESV, New King James, and others are fine too, but the more you know about the original language and original words used in your version, the better off you’ll be in understanding Scripture, and you’ll get more meaning out of the Bible. Remember, the goal of hermeneutics is to extract as much of the original meaning of the original language that we possibly can.
Here is one of the best descriptions I’ve heard about what hermeneutics really is: it is attempting to connect the Bible reader’s mind with the mind of the original author. Of course, all Scripture is inspired by God when it comes down to it (2 Tim 3:16), but each writer has a unique style and presents a distinct perspective. It’s like having four people watch a car accident. Essentially, each witness will say the same thing about the accident, but each person will have their own perspective of the incident. By reading the four gospels, we can see each of the author’s unique perspectives of the ministry of Jesus Christ. In this way, we’re getting a fuller portrait of the work of Christ on earth. When we read the Bible, hermeneutics can help us unfold a new meaning or reveal something that’s been hidden from us, and it can make obscure words more clear, and this is bassically what exegesis is. All Bible translators use hermeneutics when they are translating Scripture from one language to another.
Exegesis at Work
A good example of how exegsis works is in Acts 2 verses 4 and 11, where we read, “All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them. (Jews and converts to Judaism); Cretans and Arabs—we hear them declaring the wonders of God in our own tongues!” If we apply hermeneutics (good translations) and translate the word “tongues” from the original Koine Greek (using exegesis), it should read “All of them were filled with the Holy Spirit and began to speak in other languages as the Spirit enabled them. (Jews and converts to Judaism); Cretans and Arabs—we hear them declaring the wonders of God in our own languages!”
Another example is 1 Corinthians 14:2 where it says, “For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit.” Some translators not only didn’t apply biblical hermeneutics to this verse, but they inserted the word “unknown” as the King James Version does, and that’s eisegesis, and that’s why eisegesis is not recommended when reading the Bible. The King James translators inserted a word that they thought should be there, but wasn’t in the original manuscripts, and thus, the King James Version wrongly says, “For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries,” so the word “unknown” is not in the original manuscripts.
In short, eisegesis is inserting a meaning we or someone else thinks should be there, while hermeneutics does just the opposite; it extracts meaning from the original texts or the Bible version one is reading from what was the author’s original ideas, thoughts, or beliefs. Of course, the true Author of all Scripture is God Himself, but God truly did use these men as a means of accurately translating the very words of God…and not the words of man…which can happen when people attempt eisegesis and not good exegesis of the Bible.
Here is some related reading for you: What is Biblical Hermeneutics? What is it Important? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.