Christians have been having this same debate all throughout their earliest history and no letter that any apostle ever wrote has ever resolved those issues. That's why there's a laundry list of differing sects, Ecumenical Councils to make a collective charge of heresy, and yada yada yada.
Nobody resolved those issues then, nobody's resolved them now. As a result, we have all these different Christian sects and the following list is by no means comprehensive, there are others...
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Abelians (Abelites)
Abyssinian
Acacians (4th Century)
Adamites ("early", up to the 15th Century)
Adoptionists (8th Century)
Aerians (Aetians) (Arians) (4th Century)
Agapaemonians
Agonetae (4th & 6th Century)
Agonyclitae (7th Century)
Agynians (7th Century)
Albanois (Albanenses) (8th Century)
Albigenses (Albigois)(Gazares)(11 - 12th Century)
Albrights (Knight Evangelist Church) (1800's)
Allenites
Amedians
Anabaptists (1523)
Angelites (5th Century)
Anthromorphites
Antinomians (16th Century)
Anti-Sabbatatrians
Aphtharoocites (Eutychians)
Apollinarists (Apollinacians)(4th Century)
Apostolici (Apostolics)(Ap. Brethren)(3rd Century)(12th in Germany)
(13th in Italy, sect of Anabaptist)
Apostoolinas (Mennonites)
Aquarians (Encratites)(2nd Century)
Archonites(2nd Century)
Arians (4th Century)
Arminians
Ascites
Athanasians (4th Century)
Baptists
Barlaamites (14th Century)
Basilidians
Beghards (Beguards)(Bogards)(Bizochi)(Bocasoti)(13th Century)
Beguines (nuns)(13th Century)
Bereans (1773)
Bidellians
Bohemian Bretheren (Brothers' Union)(United Brethren)(Moravians)(15th Century)
Borrelists
Brethren (Dunkards)
Brethren (Plymouth)
Brethren (River)
Brethren (Social)
Brownists (1580)
Cainites (2ndCentury) Noteworthy:sect specifically for reprobates.
Calixtines (15th Century)
Calvinists (1500's)
Cameronians (1600's)
Camisards (1600's)
Campbellites (Disciples of Christ)(1833)
Caputiati (12th Century)
Caraites (Karaites)
Carmathites (9th Century)
Carolostadians
Carpocratians (2nd Century)
Catholic Apostolics
Catholic Charismatics
Cellites
Cerinthians
Christadelphians
Christian Church (General Christian Convention)
Christian Scientists
Christian Union
Christian and Missionary Alliance
Christians of St. Thomas
Church of England
Church of the Nazarene
Churches of Christ
Churches of God in N. Am. General Eldership
Churches of the Living God (black)
Circumcellians
Clementines
Cocceians
Collegiants (17th Century)
Colored Methodist Episcopal Church of America (separated in 1820)
Come-Outers (nondenominational)
Congregationalists (160
Copts (451 AD)
Covenanters (1600's)
Cumberland Presbyterian
Damianists (6th Century)
Dancers (Flemish group reminiscent of the Dervishes) (1700's)
Davidists (16th Century)
Donatists (4th Century)
Druses ("early"--a Mt. Lebanon thing--Turkey)
Dulcinists (14th Century)
Dunkers (Tunkers)(German Baptist Brethren)
Durisans ("early"--also a Mt. Lebanon thing, decendant of Druses--Turkey)
Dutch Reformed Church
Ebionites
Effronites (16th Century)
Elxaites
Enlish Presbyterian
Ephrath Baptists (7th Day Baptists)(172
Episcopalians
Equinians
Erastians (1500's)
Eudoxians (4th Century)
Eunomians (4th Century)
Eustathians (4th Century)
Evangelical Lutherans (Lutherans)
Evangelical Synod
Farnovians
Fifth Monarchy Men
Flagellants (Whippers)(13 thru 15th Centuries)
Fratres Albati (Fratricelli)(15th Century)
Free Thinkers
Free Will Baptists (1800's)
French Prophets (late 14th Century)
Friends (Quakers) (1600's)
Galenists
German Reformed Church
German 7th Day Baptists (172
Glassites
Gnostics (1st Century)
Gospellers (14th Century)
Greek Orthodox (15th Century)
Harmonists (1780)
Hattemists (17th Century)
Henricians (12th Century)
Heracleonites ("early")
Hermageniams (2nd Century)
Hicksites (1827)
Hoffmanists (16th Century)
Hopkinsians
Huguenots (16th Century)
Hussites (13th Century)
Hutchinsonians (1724)
Iberians (Georgians, of ancient Iberia, not the Iberian Peninsula)
Iconoclasts
Incorruptables ("under Justinian regime")
Independents (various, mainly post-Reformation)
Inghamites (18th Century)
Irvingites (1832)
Jacobites (6th Century)
Jansenists (1600's)
Keithians
Kirk (Church of Scotland)(1689)
Labadists (17th Century)
Lampetians (17th Century)
Latitudinarians (17th Century)
Leadlyans
Leucopetarians (12th Century)
Libertines (16th Century)
Lollards (associated with Wycklif)(14th Century)
Lucianists (2nd Century)
Luciferians (NOT what it looks like!)(4th Century)
Macedonians
Manicheans (3rd Century)
Marcarians (4th Century)
Marcellans (2nd Century)
Marcionites (2nd Century)
Marcites (2nd Century)
Maronites (6th Century)(another Mount Lebanon thing)
Massalians/Messalians (4th Century)
Melchisedicians (2nd Century)
Melchites
Melitoni
Menandrians (named for a BC philosopher but an AD Magistic sect)
Mengretians
Mennonites
Methodists (Wesleyan)(18th Century)
Methodist Episcopal Church (1776)
Methodist Protestant Church (182
Millenarians (Chiliasts)
Millerites (Second Adventists)(Adventists)
Molinists (17th )
Monarchians (2nd Century)
Monophysites (16th Century)
Monothelites (7th Century)
Montanists (2nd Century)
Monte-Negrins
Moravians
Mormons (1823)
Muggletonians
Neonomians
Nestorians (5th Century)
New Jerusalem Church (Swedenborgians) (1700's)
Noetians (2nd Century)
Novatians (3th Century)
Origenists (3rd Century)
Ortlibenses (Vaudois)(Waldenses) (12th Century)
Passaginians
Passalorymchites (2nd Century)
Paulianists (3rd Century)
Paulicians (6th Century)
Pelagians (5th Century)
Petrobrussians (11th Century)
Petrojoanites (12th Century)
Philipists
Pietists
Pomorians
Praxeans (2nd Century)
Presbyterians, Associate Reformed (1782)
Presbyterians, Reformed (1773)
Presbyterian Church of the United States (1716)
Protestant Episcopal Church of the United States (1785)
Progressive Friends
Psatyrians (4th Century)
Publicani (11th Century)
Puritans (Roundheads)
Puseyites (Tractarians)
Quietists ("early", Greek)(17th Century, French, Spanish Molinists)
Quintilians ("early", condemned by 2nd Century)
Re-Anointers
Rellyanists
Rogerenes (17th Century)
Roman Catholic Church
Sabbatarians
Sabellians (3rd Century)
Saccaphori (4th Century wearers of sackcloth)
Salvation Army
Sandemanians
Saint Simonians (1830)
Schwenkfeldians (16th Century)
Se-Baptists
Secularists
Seekers (17th Century)
Seleucians (4th Century)
Sembiani
Semi-Arians (4th Century)
Semi-Pelagians (5th Century)
Servetians (16th Century)
Serpentinians (Ophites)(2nd Century)
Sethians (2nd Century)
Shakers (United Society of Believers in Christ's Second Appearing)
(1770)
Six-Principle Baptists
Socinians (16th Century)
Southcottians
Starobradsi
Syrian Christians (similar to Church of England)
Tanquelinians (12th Century)
Tascodrugitae
Theodosians
Theopaschites (5th Century)
Theophilanthropists
Tractarians (1833)
Tritheists (6th Century)
Tschomaboltsi
Turlupins
Ubiquitarians
Uckewallists
Unitarians (1815)
United Brethren In Christ (1800)
Verschorists (17th Century)
Wilhelminians
Wilkinsonians (1700's)
Winebrennaarians (1830)
Wyckliffites (14th Century)
Zacheans (4th Century)
Zwinglians