Passage
Most certainly, I tell you, if a person keeps my word, he will never see death.”
John 8:51 (WEB)
Nearby Context
John 8:49 Jesus answered, “I don’t have a demon, but I honor my Father, and you dishonor me.
John 8:50 But I don’t seek my own glory. There is one who seeks and judges.
John 8:51 Most certainly, I tell you, if a person keeps my word, he will never see death.”
John 8:52 Then the Jews said to him, “Now we know that you have a demon. Abraham died, and the prophets; and you say, ‘If a man keeps my word, he will never taste of death.’
John 8:53 Are you greater than our father, Abraham, who died? The prophets died. Who do you make yourself out to be?”
Study Lenses
The verse centers on "most", "certainly", "tell", "person", "keeps", "word", "never", and "death". It is saying that the verse draws attention to "most" and "certainly", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 50's "But I don t seek my own..." into verse 52's "Then the Jews said to him Now...", so "most" and "certainly" belong inside that flow. In John context, the local focus is the identity of Jesus, new birth, eternal life, and belief and unbelief.
A plain takeaway is to answer the verse's own emphasis on "most" and "certainly" with trust shaped by these words, not by a vague optimism outside the passage.