Note, however, that he said nothing about us always being able to understand what he meant.
Well.... yes and no.
For instance, for someone who is outside of a relationship with Christ, the Bible is only so much gibberish, and our interpretation of it reflects that.
But being in Christ gives us the indwelling of the Holy Spirit and thus we can begin to understand His words, maybe not perfectly to start, but the more familiar we become with His voice, the more our understanding grows. (One Scripture that touches on this is 1 Cor 2:6-16)
Are we on the same page on this?