"These men are blemishes at your love feasts, eating with you without the slightest qualm - shepherds who feed only themselves. They are clouds without rain, blown along by the wind; autumn trees, without fruit and uprooted - twice dead." NIV translation
Now, Jude gives three examples of the actions of these so-called leaders. These men would go to the dinners held by the believers and eat their fill without regard for others. They are more concerned about themselves than they are others (the flock). That is the opposite of what Jesus did and an immediate warning sign that something is wrong. The second example is that these men are unproductive. They may look good as leaders and know how to use fancy talk but they do not share the actual Word of God. They usually talk about current events but do not give God's Word. The final example is that of "autumn trees" and that describes fruit trees at the time of harvest that don't have any fruit on them. What good is a fruit tree that does not have any fruit? These men are usually hiding sin and yet trying to lead others. They are referred to as "twice dead" in that they are dying both physically and spiritually yet trying to lead others.
"They are wild waves of the sea, foaming up their shame; wandering stars, for whom blackest darkness has been reserved forever." NIV translation
Jude continues with the description of these men and both examples from nature speak of lawless ranting and raving about things.
Just as wandering stars do not follow a set course, these men do not follow the course set by the Word of God. We see that they are deceiving themselves and their eternal place is hell. Blackest darkness refers to hell because it is a place without God and God is light. Therefore, since God is not there, there will be no light and it will be darker than you can even begin to imagine.
"Enoch, the seventh from Adam, prophesied about these men: 'See, the Lord is coming with thousands upon thousands of his holy ones to judge everyone, and to convict all the ungodly of all the ungodly acts they have done in the ungodly way, and of all the harsh words ungodly sinners have spoken against him.'" NIV translation
Jude tells us of a prophesy of Enoch. We know very little from the Bible about Enoch except that he was faithful and walked with God. He was taken by God but did not die as we read all of this in Genesis chapter five. Here, Jude tells us that, even Enoch back in Genesis, saw the second coming of Christ and the judgment of all men. He even reminds us that not only our physical actions are judged but also our words. This is very important for the false teachers that Jude has been talking to us about.