When Jesus said, “Heaven and earth will pass away, but my words will not pass away” (Mark 13:31), was He somehow saying that the Bible would be preserved?
In context, Jesus’ words in Mark 13:31 were verifying that all that would happen in Mark 13:3–30 would actually come to pass. Even if the universe were to pass away, the content of His words on the matter would not. The end-times events that He prophesied would actually come to pass.
Since Jesus was referring to His oral words in Mark 13:31, His statement does not directly teach anything about the preservation of God’s written words in Scripture. The Bible elsewhere, however, indeed teaches that God’s written words in Scripture will endure forever (Ps 119:152, 160), that is, that they will be preserved.
An indirect way to support the preservation of Scripture comes from Matthew 5:17–18. In that passage, Jesus spoke of the Mosaic Law with the same imagery seen in Mark 13:31. Not one jot or tittle (the smallest of Hebrew letters and markings) of the Law would pass away or be altered in some way unless existence itself ceased to be (cf. also Luke 16:17). Jesus’ point in Matthew 5:17–18 is that the Law could not be changed, implying its continued presence and authority. If the Law were to have a continued presence and authority, it can safely be assumed that it would be preserved in some way.
Having considered Matthew 5:17–18, we see that Jesus’ statement on the endurance of His words in Mark 13:31 effectively placed His words on the same level of Scripture itself and thus God Himself, which is obviously fitting because Jesus is God. What Jesus said would happen would happen, and nothing could change what He had promised. Likewise, what Scripture (and God) says is so, it is so, and nothing can change what Scripture says.
In short, Mark 13:31 does not speak about the written Word of God but the oral words of Jesus recorded earlier in Mark 13. But the written Word of God and the oral words of Jesus (some of which are recorded in Scripture) are indeed the same in that they are authoritative and cannot be changed or made void in any way.
The application of Mark 13:31 to Mark 13:3–30 is that we can fully expect that the events that Jesus prophesied will surely come to pass.