Jesus offers this remark in the form of a question to emphasize that his disciples will see other things that are also hard to understand. AT: "Then you will not know what to think when you see me, the Son of Man, going up into heaven!" (See: [[rc://en/ta/man/translate/figs-rquestion]])
Possible meanings are 1) "are about the Spirit and eternal life" or 2) "are from the Spirit and give eternal life" or 3) "are about spiritual things and life."