Luke omits in his version of the Olivet Discourse from Mark and Matthew the coming of false Christs who do signs and wonders

 For there shall arise false Christs, and false prophets, and shall shew great signs [σημεῖα] and wonders [τέρατα]; insomuch that, if it were possible, they shall deceive the very elect. 

-- Matthew 24:24

For false Christs and false prophets shall rise, and shall shew signs and wonders, to seduce, if it were possible, even the elect.  

-- Mark 13:22

As detailed below, Luke positively values the signs and wonders of the apostolic age. He certainly doesn't want a Jesus who throws shade on them, especially since it is really "the holy child Jesus" by whose name the signs and wonders are done.

And I will shew wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapour of smoke:  

-- Acts 2:19

Ye men of Israel, hear these words; Jesus of Nazareth, a man approved of God among you by miracles [δυνάμεσιν] and wonders and signs, which God did by him in the midst of you, as ye yourselves also know: 

-- Acts 2:22

And fear came upon every soul: and many wonders and signs were done by the apostles.  

-- Acts 2:43

And now, Lord, behold their threatenings: and grant unto thy servants, that with all boldness they may speak thy word, By stretching forth thine hand to heal; and that signs and wonders may be done by the name of thy holy child Jesus.

-- Acts 4:29f.

And by the hands of the apostles were many signs and wonders wrought among the people; (and they were all with one accord in Solomon's porch.  

-- Acts 5:12

And Stephen, full of faith and power, did great wonders and miracles [signs] among the people. 

-- Acts 6:8

He brought them out, after that he had shewed wonders and signs in the land of Egypt, and in the Red sea, and in the wilderness forty years.  

-- Acts 7:36

Long time therefore abode they speaking boldly in the Lord, which gave testimony unto the word of his grace, and granted signs and wonders to be done by their hands. 

-- Acts 14:3

Then all the multitude kept silence, and gave audience to Barnabas and Paul, declaring what miracles [signs] and wonders God had wrought among the Gentiles by them.  

-- Acts 15:12

Luke's freedom in eliding entirely the "false Christs" line at a minimum shows that the apocalyptic tradition narrated in Matthew 24, Mark 13, and Luke 21 is not yet fixed in the evangelists' own time as they struggled to reimagine and repurpose the (failed) apocalyptic material of the earlier time of the historical Jesus which lies behind it.

It has long been recognized that this apocalyptic material is a series of independent units more or less successfully woven together into a "composite discourse", but it is a "tangled skein", some elements of which might be editorial by the evangelists, some pre-existing apocalyptic either Jewish or Jewish Christian, some authentically dominical, et cetera. So Vincent Taylor, The Gospel According to St. Mark, London 2nd edition, 1966, 1977, pp. 498ff., who considers Matthew a later version of Mark, but Luke, who has "little linguistic agreement with Mk.", to be a stand alone witness presenting material from "independent" sources who must be reckoned with for the development of apocalyptic but often is not.

As Taylor recognizes, Mark's vocabulary in 13:21f. has the "later ring" of "primitive Christianity" about it. It is an apocalyptic outlook now "strange to the mind of Jesus". So it would not be odd then for Luke to exclude it, concerned as he self-consciously is to lay out his history more accurately than have other evangelists.

What we have in these apocalyptic narratives, including Luke's, is revisionism at work.

The "false Christs" idea reflects later developments, a later Christianity on the way from a Judaism which had its own false prophets, to a later Pauline world populated also by a false gospel (II Cor. 11:4; Gal. 1:6), false apostles (II Cor. 11:13), false angels (II Cor. 11:14), the son of perdition (II Thes. 2:3), and ultimately the Antichrist(s) of I and II John.

The historical Jesus, imagining the imminent end of the world in his own lifetime, would never have imagined such developments by definition.

But Luke himself hasn't thought of such things, of course, nor about the implications for either his Gospel or his Apostle (Acts, primarily about Paul). Luke's aim is to present the signs and wonders characteristic of the early and middle Pauline period as proof of his Gospel.

What is also often not considered enough is that the false Christs language of Matthew 24 and Mark 13 might actually be explicit anti-Pauline propaganda, in which case this calumny might represent the particular trigger, among other deficiencies, which motivated Luke to compose his definitive two-volume work in defense of the real Jesus and his hero Paul as he understands them, in order that his patron Theophilus "may know the certainty of those things" in which he was instructed (Luke 1:4).

Is The Absence Of Human Transformation The Best Argument Against Christianity?

A certain fellow named Robin Schumacher, featured at Real Clear Religion, goes on at some length, here, to acknowledge that the best argument that is made these days against Christianity is the one made by ever larger numbers of contemporaries who point out that Christianity must be untrue because Christians behave so badly, and concludes:

"[T]he fact is that an authentic Christian life is the only thing that defeats the best argument against Christianity."

This is a very unsatisfactory conclusion to what really isn't a very helpful discussion about arguments for or against Christianity.

What it amounts to instead is a demonstration of what passes for the accepted understanding of what is true conversion in some circles. In other words, it's not really about Christianity per se, it's about human actors and their experiences relative to that subject. In short, it's about us, not about Christianity or its object, God.

Key for the author is the notion that conversion is a form of human transformation, which can be authenticated on the evidence of human experience. "If you were truly converted you wouldn't do x."

What is it about Christianity, contemporary or otherwise, that it so quickly veers off into a kind of narcissism where adherents and opponents alike wind up agreeing that man is the measure of all things? The authentic Christian life is the only thing that defeats the enemies of Christ? I'm sure that comes as quite a surprise to God. Last I checked, God needed or depended upon no one for anything. There is sophistry. And then there is philosophy.

I think one answer for this narcissism may have something to do with what Krister Stendahl once called the introspective conscience of the West. The tortured conversion of Muhammad comes to mind in W. Montgomery Watt's biography of the prophet. Or the Jesus of The Fourth Gospel, at war with the Jews over his paternity. Or the ever autobiographical 13th apostle, Paul of Tarsus, who happens to be the most interesting because he is so immediately, candidly available in his letters as he plies the waters between his sectarianisms and his Roman citizenship. It shouldn't come as a surprise that these models would attract adherents in whom the same tendencies operate. In truth, however, thoughtful people would probably agree that narcissism is a broadly human phenomenon, not simply a characteristic of the West.

But there are counter trends in some of our literature which bear thinking about. Consider, for example, that conversion in Luke's Acts of the Apostles is occasionally portrayed as conversion of a whole household, based on the personal experience of a single person in it. For those household members personal human transformation, being born again, is hardly in sight. Even in the cases of the personal salvation of the individual head of the household who leads the rest into the fold, notions of human transformation seem wholly absent. Far from the world of altar calls involving personal crises, repentance and emotional decisions for Christ, what we find instead is concrete deliverance from temporal calamities, infirmities, threats and dangers. Like Paul's own conversion, these amount to almost unwilled experiences submitted to and accepted in the face of an overwhelming, sovereignly acting, Providence.

Some of these stories in Acts are reminiscent of nothing so much as stories of God's deliverance of his people Israel from Egyptian slavery, the plagues, the angel of death and the Red Sea waters. It is more about God continuing to act in history than it is about what happens in the hearts of men.

One might also mention the apocalyptic ethics of Jesus in The Synoptic Tradition, where personal conversion amounts to a renunciation of all the traditional contours, roles and behaviors of human existence in a desperate attempt to escape the destruction which Jesus said was coming on the world forthwith. This is not some comfortable religion of personal fulfillment, but a (crazy?) rejection of it which depends utterly on God to establish his kingdom quite apart from any human agency, even Jesus'. 

Anyone with a little honest experience of the world knows that there are many what we call very fine people who are not Christians, and many Christians who are just plain drek. If one gets bogged down in this navel-gazing cul-de-sac, however, what gets distorted about our thinking about conversion is that conversion becomes too much about how we act, and not enough about how God does.

"We also are men of like passions with you, and preach unto you that ye should turn from these vanities unto the living God, which made heaven, and earth, and the sea, and all things that are therein: Who in times past suffered all nations to walk in their own ways. Nevertheless he left not himself without witness, in that he did good, and gave us rain from heaven, and fruitful seasons, filling our hearts with food and gladness."

-- Acts 14:15ff.