Passage
For he knew not what he should say, for they were filled with fear.
For he knew not what he should say, for they were filled with fear.
Mark 9:4 And there appeared to them Elias with Moses, and they were talking with Jesus.
Mark 9:5 And Peter answering says to Jesus, Rabbi, it is good that we should be here; and let us make three tabernacles, for thee one, and for Moses one, and for Elias one.
Mark 9:6 For he knew not what he should say, for they were filled with fear.
Mark 9:7 And there came a cloud overshadowing them, and there came a voice out of the cloud, *This* is my beloved Son: hear him.
Mark 9:8 And suddenly having looked around, they no longer saw any one, but Jesus alone with themselves.
The verse centers on "knew", "should", "filled", and "fear". It is saying that the verse draws attention to "knew" and "should", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 5's "And Peter answering says to Jesus Rabbi..." into verse 7's "And there came a cloud overshadowing them...", so "knew" and "should" belong inside that flow. In Mark context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "knew" and "should" with trust shaped by these words, not by a vague optimism outside the passage.