Use of Rhetoric as a Didactive Method
Jesus makes profuse use of rhetoric, for the simple reason that such more effectively conveys and make readily retainable teachings which taught otherwise are not as memorable or impactful. That is, He does not use rhetoric to impress human persons, but to impress the teachings He wishes to on them.
Among His favorite and most used is hyperbole (or, deliberate exaggeration or use of excessive language to make a point). For example, when teaching that we must avoid the near occasion of sin (i.e. avoidable things which we know in ourselves generally lead us to sin), He teaches it in the following way:
Matthew 18:7-9 Woe to the world because of scandals. For it must needs be that scandals come: but nevertheless woe to that man by whom the scandal cometh. 8 And if thy hand, or thy foot scandalize thee, cut it off, and cast it from thee. It is better for thee to go into life maimed or lame, than having two hands or two feet, to be cast into everlasting fire. 9 And if thy eye scandalize thee, pluck it out, and cast it from thee. It is better for thee having one eye to enter into life, than having two eyes to be cast into hell fire.
To all with a more than elementary understanding of human language, it's obvious that Jesus is not here literally advocating the amputation of limbs and plucking out of eyes to avoid sin, but rather is using it as hyperbolic way of telling Chrisitans to remove the circumstance of sin which are removable, and thus, with such a removal, the chance or likelihood of sin, instead of sinnning and experiencing the circumstance of hell which necessarily must follow sin.
Wherein lies strikingness that makes the teaching memorable? In that it's infinitely and obviously easier to avoid a situation where you might sin using sight, than to pluck out your eye so that situation can never happen. This is why the teaching is so jarring and memorable. And this is why He taught it this way, and not the way in which I just explained above.
Again:
Matthew 5:33-37 Again you have heard that it was said to them of old, Thou shalt not forswear thyself: but thou shalt perform thy oaths to the Lord. 34 But I say to you not to swear at all, neither by heaven, for it is the throne of God: 35 Nor by the earth, for it is his footstool: nor by Jerusalem, for it is the city of the great king: 36 Neither shalt thou swear by thy head, because thou canst not make one hair white or black. 37 But let your speech be yea, yea: no, no: and that which is over and above these, is of evil.
What is He teaching? That a society built on honesty and trust should never have need of swearing — not that swearing will not be needed in the less-than-perfect societies in which all, including Christians, live. He is asking Christians to be honest rather than swear, not entirely forbidding the practice. The absoluteness of language is wherein the hyperbole lies, and the memorability: because any time we swear, in our imperfect societies where we can certainly not trust that yeas are yeas and nays nays (inasmuch as we cannot assume or confirm that any given person is a Christian and/or follows this perfect rule of Christ of perfect honesty), we remember that Christ wanted to do otherwise, and imagined a more perfect way for His people to live.
This is the reason He used hyperbole so much, because it is memorable, and more effective.
"Call no man your father"
Matthew 23:1-12 Then Jesus spoke to the multitudes and to his disciples, 2 Saying: The scribes and the Pharisees have sitten on the chair of Moses. 3 All things therefore whatsoever they shall say to you, observe and do: but according to their works do ye not; for they say, and do not. 4 For they bind heavy and insupportable burdens, and lay them on men's shoulders; but with a finger of their own they will not move them. 5 And all their works they do for to be seen of men. For they make their phylacteries broad, and enlarge their fringes. 6 And they love the first places at feasts, and the first chairs in the synagogues, 7 And salutations in the market place, and to be called by men, Rabbi. 8 But be not you called Rabbi. For one is your master; and all you are brethren. 9 And call none your father upon earth; for one is your father, who is in heaven. 10 Neither be ye called masters; for one is your master, Christ. 11 He that is the greatest among you shall be your servant. 12 And whosoever shall exalt himself shall be humbled: and he that shall humble himself shall be exalted.
What is this teaching? That those who love fame, honor, respect, and titles, will be humbled by God and are the least in the kingdom, because they are proud. That those who humble themselves, are the true followers of God, and the titles can be true or false when used of them, but they do not revel in said (after all, a true teacher is truly called teach, and a true Rabbi is therefore truly called Rabbi, and a true spiritual father, Father, etc.). Therefore, "Be not you called" and "Call no man" are said with respect to those who harbor and love titles themselves, and those who love to devote themselves to spiritual leaders in a disordered way, respectively.
It is not the prohitition of identifying as a spiritual father, humbly, as St. Paul, nor agreeing with or consenting to the custom of calling Elders "Father" East and West in the Church, nor, therefore, of the title "Father" in and of itself (for a title which accurately describes someone cannot be false in any way or form), but of the seeking of titles, of the reveling in them, and of the inordinate use of them with respect to mere men.
"Neither be ye called" is with respect to the desire to have yourself called, and not a prohibition of being called—period.
The immediate context makes this amply clear, as well as the New Testament witness to the meaning.
Spiritual Fatherhood in the New Testament
Jesus Himself refers to the physical and spiritual father in faith of the Jewish people as "Father Abraham":
Luke 16:24 And he cried, and said: Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, to cool my tongue: for I am tormented in this flame.
He also brought out the more spiritual aspect of this fatherhood when He implied that his "children" would do what He did (which is not to be taken for granted for merely physcial children of a man):
John 8:39 They answered, and said to him: Abraham is our father. Jesus saith to them: If you be the children of Abraham, do the works of Abraham.
Likewise St. Paul:
Galatians 3:29 And if you be Christ's, then are you the seed of Abraham, heirs according to the promise.
Romans 4:16-17 Therefore is it of faith, that according to grace the promise might be firm to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham, who is the father of us all, 17 (As it is written: I have made thee a father of many nations,) before God, whom he believed, who quickeneth the dead; and calleth those things that are not, as those that are.
So many of Jesus' teachings are misunderstood because so many are ignorant of His use of hyperbole: people confuse what He "literally" said, with what He was conveying by what He said. Hyperbole consists in the absoluteness of language, and therefore any argument against seeing it as hyperbole which relies on such things as, "But He said x, which suggests He meant it literally" overlook the very essence and substance of hyperbole.
Rather than claiming that Paul disagreed with Jesus, we should let Paul the first century Jewish follower of Jesus personally, and directly, and an acquaintance and friend of those who also met Him personally and saw Him during His ministry and afterwards when He rose, speak and tell us the meaning of the teachings of Christ. Anything else is hubris. Instead of 'Paul contradicting Jesus' maybe it's us who have misunderstood what both are saying, and how the two mutually acknowledge the validity of the other? After all, why are we, 2000 years later, in a better position to understand the teaching of Jesus than someone who conversed with the Apostles themselves, or who in any case lived 2000 years closer to the culture and freshness of the doctrine? It's simply absurd and doesn't even deserve humoring—in disagreeing with Paul's interpretation of Jesus, you are merely making yourself an alternative Paul who has at best equal claim to be able to interpret Jesus, and at worst (and in reality), no claim in comparison.