Passage
and you will bear witness also, because you have been with Me from the beginning.
John 15:27 (LSB)
Nearby Context
John 15:25 But this happened to fulfill the word that is written in their Law, ‘They hated Me without cause.’
John 15:26 “When the Advocate comes, whom I will send to you from the Father, the Spirit of truth who proceeds from the Father, He will bear witness about Me,
John 15:27 and you will bear witness also, because you have been with Me from the beginning.
Study Lenses
The verse centers on "bear", "witness", "been", and "beginning". It is saying that the verse draws attention to "bear" and "witness", so its meaning should be read from those terms before moving to application.
The prior verse says "When the Advocate comes whom I will...", giving immediate footing for "bear" and "witness". 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 "bear" and "witness" with trust shaped by these words, not by a vague optimism outside the passage.