I, like the vast majority of Christians, am relying on the fact that the exisiting earliest manuscripts are accurate copies of the originals.
They aren't, though, because in the synoptic tradition, there are no originals; just an evolving slush. Justin Martyr is recorded as as writing an apology and a dialogue with Trypho, and he's working from a different mushy version of Matthew and Luke. Apologists say that he's working from a 'harmony', but it can't be true, because often there is no parallel verse to harmonize, or clauses/words dropped, that should have been in a harmony.http://www.newadvent.org/fathers/0126.htm
<-- First Apologyhttp://www.newadvent.org/fathers/0128.htm
Looking at the gospel that JM is apparently quoting from, and comparing it to the modern versions, you can see that the quotes are just composed the way the current redactor feels they should be arranged, like a musical arrangement. The Qumran scrolls verified that some books of the OT were very similar to the Masoretic texts, but others had variants.
The fact that we have Matthew/Mark/and JM's text/Luke (4 synoptic variants) shows that no section of the synoptic can be trusted to verse-level accuracy. Further, the modern Matthew and Luke seem to be derived from JM's version, rather than a 'harmony'. Matthew is a much more bloated expansion on JM's version. Subtle word changes show that it's not just JM dropping bits for brevity.
I've put the quotes from JM in blue, followed by quotes from Matthew or LukeMany false Christs and false apostles shall arise, and shall deceive many of the faithful.' Matthew 24:11
 And many false prophets shall rise, and shall deceive many.'The law and the prophets were until John the Baptist; from that time the kingdom of heaven suffers violence, and the violent take it by force. And if you can receive it, he is Elijah, who was to come. He that has ears to hear, let him hear.' Matthew 11:12-15
 And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force.
 For all the prophets and the law
prophesied until John.
 And if ye will receive it, this is Elias, which was for to come.
 He that hath ears to hear, let him hear.
(law and prophets is the Lukan distortion)'Many shall say to Me in that day, Lord, Lord, have we not eaten, and drunk, and prophesied, and cast out demons in Your name? And I will say to them, Depart from Me.' Matthew 7:22
 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?'Depart into outer darkness, which the Father has prepared for Satan and his, angels.' Matthew 25:41
 Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:'The Son of man must suffer many things, and be rejected by the Scribes and Pharisees, and be crucified, and on the third day rise again.' Luke 9:22
 Saying, The Son of man must suffer many things, and be rejected of the elders and chief priests and scribes, and be slain, and be raised the third day.They shall neither marry nor be given in marriage, but shall be equal to the angels, the children of the God of the resurrection.' Luke 20:35f.
 But they which shall be accounted worthy to obtain that world, and the resurrection from the dead, neither marry, nor are given in marriage:
 Neither can they die any more: for they are equal unto the angels; and are the children of God, being the children of the resurrection.'No man knows the Father but the Son; nor the Son but the Father, and they to whom the Son will reveal Him.' Matthew 11:27
 ... and no man knoweth the Son, but the Father; neither knoweth any man the Father, save the Son, and he to whomsoever the Son will reveal him.If you love them that love you, what new thing are you doing? For even fornicators do this.
 For if ye love them which love you, what reward have ye? do not even the publicans the same?Give to him that asks, and from him that would borrow turn not away; for if you lend to them of whom you hope to receive, what new thing are you doing. Even the publicans do this.
 Give to him that asketh thee, and from him that would borrow of thee turn not thou away. (missing next statement)"Take no thought what you shall eat, or what you shall put on: are you not better than the birds and the beasts? And God feeds them. Take no thought, therefore, what you shall eat, or what you shall put on; for your heavenly Father knows that you have need of these things. But seek the kingdom of heaven, and all these things shall be added unto you. For where his treasure is, there also is the mind of a man." And, "Do not these things to be seen of men; otherwise you have no reward from your Father which is in heaven." Matthew 6:1
 Therefore take no thought, saying, What shall we eat? or, What shall we drink? or, Wherewithal shall we be clothed?
 (For after all these things do the Gentiles seek:) for your heavenly Father knoweth that ye have need of all these things.
 But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.
 Therefore I say unto you, Take no thought for your life, what ye shall eat, or what ye shall drink; nor yet for your body, what ye shall put on. Is not the life more than meat, and the body than raiment?
 Behold the fowls of the air: for they sow not, neither do they reap, nor gather into barns; yet your heavenly Father feedeth them. Are ye not much better than they?
 Which of you by taking thought can add one cubit unto his stature?
 ...Take no thought for your life, what ye shall eat; neither for the body, what ye shall put on.
 The life is more than meat, and the body is more than raiment.
 Consider the ravens: for they neither sow nor reap; which neither have storehouse nor barn; and God feedeth them: how much more are ye better than the fowls?
 And which of you with taking thought can add to his stature one cubit?
 If ye then be not able to do that thing which is least, why take ye thought for the rest?"Fear not them that kill you, and after that can do no more; but fear Him who after death is able to cast both soul and body into hell." Matthew 10:28
 And fear not them which kill the body, but are not able to kill the soul: but rather fear him which is able to destroy both soul and body in hell."Behold, you shall conceive of the Holy Ghost, and shall bear a Son, and He shall be called the Son of the Highest, and you shall call His name Jesus; for He shall save His people from their sins,"
 And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David:
 And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
 But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost.
 And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from their sins.To him that smites you on the one cheek, offer also the other; and him that takes away your cloak or coat, forbid not.
 But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right
cheek, turn to him the other also.
 And if any man will sue thee at the law, and take away thy coat, let him have thy cloke also.And whosoever shall be angry, is in danger of the fire.
That whosoever is angry with his brother without a cause shall be in danger of the judgment:"Swear not at all; but let your yea be yea, and your nay, nay; for whatsoever is more than these comes of evil." Matthew 5:34, 27
 But I say unto you, Swear not at all; neither by heaven; for it is God's throne:
 Nor by the earth; for it is his footstool: neither by Jerusalem; for it is the city of the great King.
 Neither shalt thou swear by thy head, because thou canst not make one hair white or black.
 But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil."For many shall come in My name, clothed outwardly in sheep's clothing, but inwardly being ravening wolves. By their works you shall know them. And every tree that brings not forth good fruit, is hewn down and cast into the fire."
 Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves.
 Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles?
 Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.
 A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.
 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.
 Wherefore by their fruits ye shall know them..