Who is a Samaritan (Hebrew) believer?

Who is a Samaritan (Hebrew) believer?

The answer the question of who is a Hebrew believer is exactly the same as for the questions of who is a Jew, a Christian, or a Muslim believer. And what would that answer be? That “the Tree is known by it’s fruits”!
In other words, if your lifestyle bears witness to the fact that the supreme standard for all of what you say, do, or think are the life, teachings, and actions ascribed [by God’s Law] to Moses, then you are indeed a true Hebrew believer; if it is instead the life, teachings and actions ascribed [by the Gospels] to Jesus, then you are a Christian believer; Finally, if it is the life, teachings and actions ascribed [by the Qur’an] to Muhammad, then you are a Muslim believer.
As for the theological differences between these monotheistic traditions, it would be wise to remember that, in the eyes of God, it is “our fruit” what really matters, as God gives much more importance to our personal morality, than to our personal theology.
And the former is clearly attested by king David, when he goes on to say that the righteous will abide in God’s holy mountain, regardless of their personal theology; As is written:
“Lord, who shall dwell in thy Tabernacle? who shall rest in thine holy Mountain? He that walketh uprightly and worketh righteousness, and speaketh the truth in his heart. He that slandereth not with his tongue, nor doeth evil to his neighbor, nor receiveth a false report against his neighbor. In whose eyes a vile person is contemned, but he honoreth them that fear the Lord: he that sweareth to his own hindrance and changeth not. He that giveth not his money unto usury, nor taketh reward against the innocent: he that doeth these things, shall never be moved”- Psalm 15: 1-5 (1599 Geneva Bible).

The God of the Hebrew Bible isn’t an ideological dictator, nor is He a Religious Tyrant

The Supreme God preached by our master Moses [blessed be He] isn't an ideological dictator, nor is He a religious tyrant who says: " It's my way, or the highway" [In other words, either you do, say, and believe exactly as I demand, or else you are doomed! ].
And that's why we often find the Creator “setting up the stage” in such a way as to allow His stern judgment [as well as His manifested will] to be “conquered” [or “swayed”] by the human plead for mercy and compassion.
And this is what happened to king Hezekiah, who after being told that he would die, was told instead the following, “... Thus saith the Lord, the God of David thy father, I have heard thy prayer, I have seen thy tears: behold, I will heal thee: on the third day thou shalt go up unto the house of the Lord”- 2 Kings 20: 5, KJV.
And something similar could have happened to Sodom-- God would have pardoned it, had He found at least 10 righteous men inside of it. As is written, “And he [Abraham] said, Oh let not the Lord be angry, and I will speak yet but this once: Peradventure ten shall be found there. And he said, I will not destroy it for ten's sake”- Genesis 18: 32, KJV.
In short, God’s mercy always prevails upon His stern judgment, so that humans are never paid according to their wickedness (“He hath not dealt with us after our sins; nor rewarded us according to our iniquities. For as the heaven is high above the earth, so great is his mercy toward them that fear Him”- Psalm 103: 10-11, Christian Standard Bible).
And the former might explain the reason why, though God had told Adam that he would die the very day he ate of the tree (“But you must not eat from the tree of the knowledge of good and evil, for on the day you eat from it, you will certainly die”- Genesis 3: 17, C. S. B. ), Adam was allowed to live almost 1, 000 additional years (“So Adam’s life lasted 930 years; then he died”- Genesis 5: 5, CSB).
Likewise, though the Creator had cursed the Ground (“And He said to the man… The ground is cursed because of you” - Genesis 3: 17, C. S. B. ), the latter was still fruitful enough to feed the whole mankind.
Finally, although God had cursed the woman (“He said to the woman: I will intensify your labor pains; you will bear children with painful effort. Your desire will be for your husband, yet he will rule over you” - Genesis 3: 16, C. S. B. ), when the latter is pretty, everybody runs after her.

In what sense was Christian theology foreshadow by the story of King Saul?

Truth be told, Christian religion is an awesome faith, and Christian believers have absolutely nothing to envy from their Hebrew counterparts (Jews, Samaritans, Karaites, Noahides, etc). Unfortunately, you will find that Christian theology is often at odds with the most basic tenets revealed by God's Law. Consider the example of people speaking different languages (“speaking in tongues”)-- While the gospel presents the latter as a sign of God's blessing and approval upon the believers [during Pentecost, at the upper room], God's Law portrays it as the result of God's curse [and disapproval] against the rebellious unbelievers [at the tower of Babel].
Consider a second example: While the gospel portrays physical circumcision as equivalent to not being part of God's flock (“For I testify again to every man that is circumcised, that he is a debtor to do the whole Law. Christ is become of no effect unto you, whosoever of you are justified by the Law; ye are fallen from Grace”- Galatians 5: 3-4, KJV), God's Law portrays it as being the opposite (“And the uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people; he hath broken my covenant”- Genesis 17: 14).
Finally, consider the example of taking oaths-- While God's Law commands the believer to make his oaths using God's name (“Thou shalt fear the Lord thy God... and shalt swear by His name”- Deuteronomy 6: 13), The gospel teaches the opposite, as the latter forbids the believer from making any oath (“But I say unto you, Swear not at all”- Matthew 5: 34).
And a similar analysis could be made for almost each single tenet comprising Christian theology; always arriving at the same result-- that, although a godly and valid religion, Christianity encourages it’s followers to think [and behave] in a way that directly opposes God's Law. In fact, it makes them oppose God's Law in such a clever way that most Christian sincerely believe they are actually doing the opposite (fulfilling the Law’s truest and deepest meaning! ).
In this sense, it could be properly said that Christianity was foreshadowed in the story of king Saul; who, while openly disobeying the word of God brought upon him by prophet Samuel (to destroy Amalek, including all of it's cattle), dared to claim the opposite (that he had actually obeyed God's word! ). As is written: “… and Saul said unto him, Blessed be thou of the Lord: I have performed the commandment of the Lord. And Samuel said, What meaneth then this bleating of the sheep in mine ears, and the lowing of the oxen which I hear? ”- 1 Samuel 15: 13-14.
Sadly, just as Saul's rebellion [against the word of God] resulted in Israel being led by a man troubled by an evil spirit (“But the Spirit of the Lord departed from Saul, and an evil spirit from the Lord troubled him”- 1 Samuel 16: 14), so did Saul of Tarsus rebellion [against the word of God] resulted in Christianity being led by a man troubled by an evil spirit (“... there was given to me a thorn in the flesh, the messenger of Satan to buffet me, lest I should be exalted above measure”- 2 Corinthians 12: 7).
May the Almighty bless and guide the hearts and minds of our beloved Christian brothers and sister!