Ether 3:13-19 Because thou knowest...

13 And when he had said these words, behold, the Lord showed himself unto him, and said: Because thou knowest these things ye are redeemed from the fall; therefore ye are brought back into my presence; therefore I show myself unto you

If faith is a hope for things which are not seen, but which are true, then based on the quote above,  the brother of Jared was beyond faith even upon his initial conversation with the Lord. Christ said, "Because thou knowest these things...I show myself unto you" (Ether 3:13). Jared's brother knew. He didn't hope, and it didn't matter that the Lord was not seen; somehow, all that mattered to him was that he had witnessed enough to know God the Son.

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 14 Behold I am he who was prepared from the foundation of the world to redeem my people. Behold I am Jesus Christ. I am the Father and the Son. In me shall all mankind have life, and that eternally, even they who shall believe on my name; and they shall become my sons and my daughters. 

What does it mean to be both the Father & the Son? The footnote next to the word "Father" directs readers to Mosiah 15:2-4, which reads,

"And because he dwelleth in the flesh he shall be called the Son of God, and having subjected the flesh to the will of the Father, being the Father and the Son - The Father, because he was conceived by the power of God, and the Son, because of the flesh; thus becoming the Father and Son - And they are one God, yea, the very Eternal Father of heaven and of earth."

So in addition to being conceived by Heavenly Father's power, it is Christ's submission to God's will is what makes Him both "the Father and the Son." Specifically, it's the flesh seems to play a key role, likely because it was necessary for Christ to live on earth in order to act according to God's will.

Could it also be that, the fact that the Savior created both the Heavens and the earth makes him a "Father?" He created life under Heavenly Father's supervision; the creation of life makes him a father.

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Two other scriptures of importance...

15 And never have I showed myself unto man whom I have created, for never has man believed in me as thou hast. Seest thou that ye are created after mine own image? Yea, even all men were created in the beginning after mine own image.

19 And because of the knowledge of this man he could not be kept from beholding within the veil; and he saw the finger of Jesus...and he had faith no longer, for He knew, nothing doubting. 

 Just as the First Vision provided us with the knowledge of Heavenly Father and Jesus Christ's bodies, so too does the brother of Jared's account of Christ. What's most remarkable is that Jared's brother was the first up to that point to ever have seen Christ's body.

A final point: once again, notice how important the brother of Jared's absolute knowledge of Christ is. The Lord tells him that He revealed Himself to him because he "believed in me as thou hast," and "He knew, nothing doubting" (Ether 3:15; 19).