Passage
this one came for testimony, that he might testify about the Light, that all might believe through him;
this one came for testimony, that he might testify about the Light, that all might believe through him;
John 1:5 and the light in the darkness did shine, and the darkness did not perceive it.
John 1:6 There came a man--having been sent from God--whose name <FI>is<Fi> John,
John 1:7 this one came for testimony, that he might testify about the Light, that all might believe through him;
John 1:8 that one was not the Light, but--that he might testify about the Light.
John 1:9 He was the true Light, which doth enlighten every man, coming to the world;
The verse centers on "light", "came", "testimony", "might", "testify", "believe", and "through". It is saying that the verse draws attention to "light" and "came", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 6's "There came a man--having been sent from..." into verse 8's "that one was not the Light but--that...", so "light" and "came" 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 "light" and "came" with trust shaped by these words, not by a vague optimism outside the passage.