Mat 7:13 Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat:
Mat 7:14 Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it.
(e-Sword:KJV)
Jesus was so stupid, He didn't make provision to protect billions and billions of people from getting His message ALL WRONG and therefore going to HELL!
Mat 23:15 Woe unto you, scribes and Pharisees, hypocrites! for ye compass sea and land to make one proselyte, and when he is made, ye make him twofold more the child of hell than yourselves.
If it is true that ONLY Scripture is the source of truth about God [...]
The OP did not say 'ONLY', nor does sola-scriptura. 'Supreme authority' is not 'only'. Try again.
One ought to look at the context of the verses. The gospel went over like a lead balloon among the Jews. That could possibly be “the few” being referred to. The gospel later got a much heartier reception among the gentiles, who didn’t have a long religious tradition to be proud of and be a stumbling block. At any rate it is the Shepherd who can (and will, if believed upon) get you through the narrow gate. And no matter what other things you also mistakenly believe, if you’ve come to the Shepherd and the Shepherd has you, you’ll get through the gate — maybe it will be a painful journey as he yanks you out of the waters, but you’ll get through it. That has nothing to do with a sign over a worship building. (Sometimes I have to chide Protestants that they aren’t being Protestant enough, that they dip into Catholic beliefs that the doctrine saves you... nope it’s the Person of Christ. Protestant doesn’t mean being a better flavor of Catholic.)