The Bible includes many examples of where prophets prophesy in the present tense or as if the things in the prophecy have already occurred. For example, rather than saying “Christ will come” they would say “If Christ did not come”. This is known as prophetic perfect.
An example from the Bible is in Isaiah 53:3-5 which says:
He is despised and rejected of men; a man of sorrows, and acquainted with grief: and we hid as it were our faces from him; he was despised, and we esteemed him not. Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted. But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed
We see examples of prophetic perfect in the Book of a Mormon too such as in Mosiah 16:16:
And now if Christ had not come into the world, speaking of things to come as though they had already come, there could have been no redemption.
Why would Joseph Smith have spoken in this tense? How would he know about prophetic perfect?