Beliefs and Doctrine
Thank you for your question. Although you may be satisfied with authentic reports (perhaps not all at the level of tawatur) to construct your framework of belief, it is more common to start from an intellectual starting point. Aqaed is generally taught through a number of intellectual proofs for the existence of God, followed by an intellectual discussion on His Attributes in the light of the scriptural sources and then proofs for Prophethood, Imamate and Resurrection. At the same time, religious experience plays an important role in reaching certainty in what one believes. In short, a combination of the scriptural sources, the intellect and religious experience that contribute to the framework of belief. This is why taqlid is not required when it comes to belief.
May you always be successful
Another thing to consider is that the verse is about people, not doctrines. That is, the verse is not offering a view on Judaism, Christianity, or Sabaeanism.
Rather, the point of the verse is that, in the afterlife, individuals will be judged according to their inner and outer realities and whether they have purified or destroyed their souls, not their worldly identities. It is not enough simply to say "I'm a Christian!" or "I'm a Muslim!" and expect salvation.
Also, the verse is advising us not to be arrogant about our religious identity.
This verse refers to the followers of previous religions who followed their original religion before distortion and deviation. Every believer must follow the prophet who has been sent after his previous prophet, otherwise he will be disobeying Allah (SWT). The Jewish believer Must believe in Prophet Easa (Jesus) when he was sent, and every Christian believer must believe in Prophet Muhammad (SAWA) when he was sent by Allah (SWT).