Paul's ability and learning made him at that time the most learned of the young rabbis (teachers). In fact in his testimony before King Agrippa, (Acts 25 and 26), he made a point of mentioning that he had been taught by Gamaliel, who was one of the most revered teachers of the Law ever in Israel. His head knowledge was beyond dispute, and together with his even more important quality, (his heartfelt dedication), led him to persecute to death the early Christians. These very qualities, (particularly the Lord's knowledge of his sincere and dedicated heart), led to that most favoured of pronouncements from the Lord; "he is a chosen vessel"! (Acts 9:15). Also, as shown in his testimony before King Agrippa; Paul showed his constant contact with the Risen Jesus; and that his mission was guided and adjusted over time; see below and Apostle Paul's Accusers.
John the Baptist, Jesus and the Apostle Paul berated the Jewish Hierarchy of the day for adhering to the Pharisaic writings, instead of the Originals given to Moses, known as "Biblical Judaism". It is recorded and well known by the Jews, that the Pharisees in particular were "very flexible" in their interpretations of Torah, and this is confirmed by the Qumran Scrolls. Of the main 'schools', or Groups of the day, the Pharisees, the Sadducees and the Essens; the Pharisees became dominant, and at the time of the destruction of the Temple in AD 70, only the "Judaism of the Pharisees", known as "Rabbinic Judaism" prevailed! This grew, and by AD 300, all the Pharisaic Interpretations of the original over centuries of “study by Jewish Sages” had been tabulated in the "Mishnah", purported to show the “original Scriptures”, with the Pharisaic “interpretation”. See: Jewish Scriptures: This is the basis of "Modern (Orthodox) Judaism".
This is why the Truths of the Messiah of Almighty God, as depicted and prophesied in the "Biblical Judaism" of the Old Testament (OT), are not accepted by the Jews who adhere to the current "Rabbinical Judaism" which is as said derived from the Pharisees.
Paul made it clear at his trial before King Agrippa, that at his encounter with the Risen Christ on the Damascus road, that He (Christ) would be in constant contact with him, and that there would be initial instructions, and that later instructions would be forthcoming from Christ. The fact of later instructions, shows that a state of flux existed with the Jews at the time of the Damascus Road encounter! (See above link ‘Paul’s Accusers’).
Those latter instructions were withheld until the Jews had finally rejected Christ, at the last of the Synagogues in Rome (Acts 28:25-27). It is well known that individual Jews become Christians, then and now. However, for the Jewish Nation to be fully in God's favour and fulfilled as per prophecy, the Ruling Groups (the Elite) must accept "Him whom they pierced” (Zech. 12:10), and when that happens, then "National Israel" will be reborn, and all the promises of Jehovah God relative to them will start to be fulfilled, including the land borders promised, and the formation of the “ideal Israel”; (Deut. 32:15, 33:26; 33:5 & Isa. 44:2).
When National Israel rejected Christ as Messiah at Acts 28:25-27, Paul immediately turned to the Gentiles, in the profound statement in Acts 28:28, which indicated the change in the Administration (Dispensation)! That point also was when Paul could no longer heal on request, (2Tim. 4:20) as the Jewish race became "Lo Ammi", (not My people), and the special powers given for the drawing together and teaching of that people, declared by Peter at Pentecost, ceased. (See: Bible Dispensations).
It is argued by some that there is no proof in Scripture that Paul had such healing powers, but Acts 19:5-15, shows otherwise, amongst many other verses! The power for "spiritual gifts" that was evident with the Jews in Acts etc. has ceased, in the sense of their then manifestation. That was exclusively God's Jewish dealings. The Holy Spirit does act now through people and events, but not in the same way, and not for the same reasons and effect. There will be quite similar happenings when the events of Revelation are current, but the prime object then will again be the Jewish Nation, in the contest between Satan and Jehovah Zebaoth, (see: Satan's Contest with God), on a much larger scale, but reminiscent of the spiritual battle between Moses and Pharaoh.
There is a continuing emphasis in "Churches" and sects, to apportion to themselves those things which properly belong to the Nation of Israel, when God is dealing with them as a Nation; instead of realising that the Gospels and the early Acts period are in fact a continuation of the Old Testament, and a propagation of the New Testament, offered by Christ to His people the Jews!
The final rejection of Christ as Messiah at Acts 28:26-30, and the rejection of the New Covenant by Israel, introduced the Gentiles for the first time as the prime object of God's Mercy and Plan! Acts 28:28 states; "Be it known therefore unto you, that the Salvation of God, is sent unto the Gentiles, and that they will hear it”. Paul is here speaking to the Roman Jews, vs 25-27, but by extension to all Israel!
That critical point specifically started the "Age of Grace", which is still in play, when "all who will, may come" (to Christ Jesus) from Gentile and Jew! Some Christians object to the above Acts 28:28 statement, saying that the Gentiles were included in the statement in Acts 15:17. However; a careful reading of Acts 15:16-17 shows that it refers to the post re-establishment of David’s “house” or Reign; which would have taken place at the acceptance of Christ Jesus as their Messiah! As the Jews did not take that crucial step; it is now delayed until after the Second Advent of Messiah Jesus in the yet future. (Current date Dec. 2016).
At that future time; Jeshuran (Ideal Israel) will become a “Kingdom of Priests unto God”; residing in Jerusalem and the future Israel of the borders promised by God in Gen. 15:18.
The Jew though has an inability to "see clearly", God has placed a veil over their understanding due to their rejection of Jesus (2Cor. 3:14), at this present time, which will be removed at a later date, when they become "Ammi", (My people) again.
In this the present Dispensation, all people of all races can be Saved from destruction because of their sin and sin nature, and is the free gift of God in Christ's substitutionary death on the cross of Calvary, which God the Father accepts as sufficient for all sin! This Great Salvation can be obtained now! All that is required is the sincere decision by a person, which can only be genuine, for this most wondrous of gifts to be obtained! This offer is still available, and has been for nearly 2000 years, but will only last for a definite period of time. That timing is in the hands of God the Father, and many think that it will be withdrawn soon, as the events of prophecy in the Middle East start to take place regarding Israel!
The last seven of Paul's writings (Eph., Phil., Col., Tim. 1 & 2, Titus, and Philemon), give the change of emphasis in the Gentile period, which is from Acts 28:28, until sometime in the future, when the Body of Christ is taken to Him, (The Rapture). See: THE RAPTURE of Christians and Overcomers & The Rapture Those Taken and Those Not.
It is the writers opinion that this takes place prior to "Ammi", (My people) condition of the Jews, but there is much dispute and difference of opinion on this. A most possible timing is at the same time as Christ rescues His Remnant people Israel.
In Conclusion, Paul was a "chosen vessel", (Acts 9:15), because of his great learning under Gamaliel; and the fact of his sincere heart before God! He had the knowledge and force of personality to take on the Jews, both Pharisaic and those converted to Christ Jesus; when dealing with the long established rituals of Judaism; such as sacrifice, circumcision etc., which were no longer required by God the Father due to the Sacrifice of Jesus (Eph. 2:15); the perfect man (Lamb without spot or blemish) for those that believe! Also; to give Israel guidance and understanding, the understanding; they needed of the "New Covenant" (Jer. 31:31- 37) had they accepted Christ as Messiah, to guide them into the "Kingdom Age".
Had they accepted Paul's message and Christ; John the Baptist would have "been as Elijah" (Matt.11:14 and 17:9-13), as Jesus stated. When they rejected, he became almost 100% "the Apostle to the Gentile" (Romans 11:13). This statement refutes the oft made comment by some Church leaders and teachers, that "Paul's teaching, and Christ's teaching contradict", (see above Link).
It is a profound truth, that Paul was the mouthpiece of Christ after His resurrection, and therefore the words of Paul are the words of Christ Himself! To understand that, is to see that Paul's words must be revered and used for understanding of the complex events following Pentecost, and the events that Peter was describing! When it is realised that Paul's words are Christ's Words, a new impetuous and accuracy is added to the interpretation of the Bible, in the sense that instead of Christ's and Paul's teachings appearing to conflict, as so many Churches teach, they are interwoven in the Truth of the Word! The onus is on us to see the real meanings!