What is purpose of being ready for the End Times? I have seen Christians study the Scriptures for clues as to how one can tell that the Second Coming, the Tribulation, the events of Revelation, the End Times are upon us. 

What is the purpose for such preparation? Would it be to stop participation in a particularly bad sin? To be able to point things out to weaker-faith faith family members so that they can get assurance Bible is true?  What have prominent theologians who hold to the importance of an End-Times theology written about the necessity of preparation, or action upon knowing the signs (as opposed to everyday duties for Christians)?

Here, one theologian that doesn't fit this criteria would be Martin Luther, or others who might say it's an allegory.
The purpose for preparation of the second coming is made clear throughout the New Testament.  There are three related primary effects:

It holds you accountable for your actions (2 Peter 3)

It keeps you from living too closely attached to a fallen world. (Hebrews 11)

It reminds you that your work is for the unseen Master, and that there will be a reward (Jesus' parables)


And note, 2 Thessalonians points would what this should look like.  It isn't about trying to figure out &quot;the day or the hour,&quot; but rather leading a blameless life so that the master will be happy when he returns.
Finally, Jesus' parables often talk about being prepared for the return of the Master.  Be it the parable of the Wedding Guests, or the Foolish Virgins, the Talents, or the Wheat and the Tares, being found ready when the Master returns is always commended.  Indeed, Jesus specifically says in Matthew 24:

36 “But about that day or hour no one knows, not even the angels in heaven, nor the Son,[f] but only the Father. 37 As it was in the days of Noah, so it will be at the coming of the Son of Man. 38 For in the days before the flood, people were eating and drinking, marrying and giving in marriage, up to the day Noah entered the ark; 39 and they knew nothing about what would happen until the flood came and took them all away. That is how it will be at the coming of the Son of Man. 40 Two men will be in the field; one will be taken and the other left. 41 Two women will be grinding with a hand mill; one will be taken and the other left.
42 “Therefore keep watch, because you do not know on what day your Lord will come. 43 But understand this: If the owner of the house had known at what time of night the thief was coming, he would have kept watch and would not have let his house be broken into. 44 So you also must be ready, because the Son of Man will come at an hour when you do not expect him.
45 “Who then is the faithful and wise servant, whom the master has put in charge of the servants in his household to give them their food at the proper time? 46 It will be good for that servant whose master finds him doing so when he returns. 47 Truly I tell you, he will put him in charge of all his possessions.


In 2 Peter 3, we read this:

Above all, you must understand that in the last days scoffers will come, scoffing and following their own evil desires. 4 They will say, “Where is this ‘coming’ he promised? Ever since our ancestors died, everything goes on as it has since the beginning of creation.”  ... 8 But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day. ... 10 But the day of the Lord will come like a thief.

This then begs the question:

11 Since everything will be destroyed in this way, what kind of people ought you to be? You ought to live holy and godly lives 12 as you look forward to the day of God and speed its coming. That day will bring about the destruction of the heavens by fire, and the elements will melt in the heat. 13 But in keeping with his promise we are looking forward to a new heaven and a new earth, where righteousness dwells.
14 So then, dear friends, since you are looking forward to this, make every effort to be found spotless, blameless and at peace with him.

Likewise, the author of Hebrews commends those who are detached from this world.  The author specifically points out those who lived as &quot;aliens and strangers&quot; for special value in faith, writing:

13 All these people were still living by faith when they died. They did not receive the things promised; they only saw them and welcomed them from a distance, admitting that they were aliens and strangers on earth. 14 People who say such things show that they are looking for a country of their own. 15 If they had been thinking of the country they had left, they would have had opportunity to return. 16 Instead, they were longing for a better country—a heavenly one. Therefore God is not ashamed to be called their God, for he has prepared a city for them.

By longing for that which is to come, these people are specifically showing they value God above the world.