When a called out one is fulfilling pisteuo correctly, and eventually recieves the Spirit of Christ, he has the ability to stand alone and lack nothing, that's is God's primary purpose for the called. The being taught other truths could be for specific purposes beyond His hope for every called out one.
The other truths would be mostly taught by " the gifted teachers" identified in Eph 4, discerned by the Spirit of Christ inside.
We fulfill saving faith that comes by God's grace (unmerited favor) through Christ Jesus who is our hope of saving faith as we believe He is the only begotten Son of God, being the word of God come in the flesh of man. God has raised Him from the dead and now sits at the right hand of the Father who is our mediator before Him in all righteousness. There is only one truth that only comes by the Holy Spirit sent down by God after Jesus ascended up to heaven who teaches and bares witness of the word of God in all truth that no man apart from the Holy Spirit can teach us nothing.
John 14:26 But the Comforter,
which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
John 16:13 Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear,
that shall he speak: and he will show you things to come. 14 He shall glorify me: for he shall receive of mine, and shall show
it unto you. 15 All things that the Father hath are mine: therefore said I, that he shall take of mine, and shall show
it unto you.
If one can not understand this then they have not the Spirit of Christ in them through the Spiritual rebirth from above and are none of His own as the Spirit of Christ is the Holy Spirit that is the Spirit of God within Deity of the Godhead.