In this context, "eloquent" describes a man well-educated, reinforcing his arguments with many appeals to logic and to outside authorities. Whether the Book of Hebrews was written by Apollos or not, it is a blow-for-blow example of the kind of ultra-sophistication that Luke ran into, in Acts 18:24-28.
In Hebrews 3, the inspired writer points out that with all of the other things that Jesus accomplished, He was also the greatest Apostle of all time:
Heb 3:1 Wherefore, holy brethren, partakers of the heavenly calling, consider the Apostle and High Priest of our profession, Christ Jesus;
Heb 3:2 Who was faithful to him that appointed him, as also Moses was faithful in all his house.
Heb 3:3 For this man was counted worthy of more glory than Moses, inasmuch as he who hath builded the house hath more honor than the house.
Heb 3:4 For every house is builded by some man; but he that built all things is God.
Heb 3:5 And Moses verily was faithful in all his house, as a servant, for a testimony of those things which were to be spoken after;
Heb 3:6 But Christ as a son over his own house; whose house are we, if we hold fast the confidence and the rejoicing of the hope firm unto the end.
Literally, an "apostle" is one "sent forth," a messenger, an ambassador. But the word is pregnant with importance. If you send your daughter to the store to buy some ice cream, she's sent forth, but she's not an apostle.
"Apostle" carried the power then, that the word "Quest" does now. Frodo was an Apostle of Gandalf -- he had a mission, to pitch the ring into the volcano, and don't come back until you do. Sir Galahad was an Apostle of King Arthur -- find the Grail, and come back with your shield or on it. There is no turning back for an apostle.
In real life, Neil Armstrong was an Apostle of NASA. It wasn't like he was going to get to 50,000 miles altitude and then go, "Ahhhh, I'm not in the mood. Let's head to Mars or back to the Earth. Who cares about a few moon rocks?" Armstrong was to run some experiments on the moon, was to bring back some materials, plant a flag, and once he was strapped into the chair, he was there until he had successfully finished up.
The apostle Paul had a mission: take the good news to the Gentiles in Asia Minor. It was a quest, a geas. You don't have to find a Bible to answer the question of whether he slam-dunked that mission. Your local university library probably has 1,000 to 10,000 books on the Apostle Paul and the way that his quest changed the planet.
The Jews had a beloved apostle, that being Moses. Moses' quest was not to bring down the ten commandments: Moses' quest was to bring Jewish slaves out of Egypt. Did he accomplish it? Not only Biblical, but secular, history records the Jews' history in a land that was north of the Nile river.
The Jews loved Moses: "Though are His (Jesus') disciple: but we are Moses' disciples" (John 9:28). But the Hebrew writer gently, in a friendly manner, points out an Apostle who could do far more for them than even Moses had.
Jesus' mission? To reconcile man to God. To heal a breach. To offer a new start to every human being on Earth. That's the "Apostle and High Priest" part of it: when we've messed up reallllly badly, how do we fix it? The High Priest helps us fix things that have been broken beyond repair.
Once Jesus accepted the mission, left the paradise, was ripped from the Father's side and ripped from ultimate Love, then He was on a mission of no return. Get the planet healed, period.
From a spiritual or secular standpoint, the Mission that Jesus Christ accepted was mind-boggling. Supposing that there were a parallel Earth on which Jesus never lived and died ... and that on this Earth, perhaps, the Roman Empire had therefore never perished under the burden of suppressing Truth and Freedom.
On a non-Jesus Earth, how close would mankind have been to God?
Consider our Apostle.