Passage
And now I have told you before it come to pass, that, when it is come to pass, ye might believe.
John 14:29 (KJV)
Nearby Context
John 14:27 Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid.
John 14:28 Ye have heard how I said unto you, I go away, and come again unto you. If ye loved me, ye would rejoice, because I said, I go unto the Father: for my Father is greater than I.
John 14:29 And now I have told you before it come to pass, that, when it is come to pass, ye might believe.
John 14:30 Hereafter I will not talk much with you: for the prince of this world cometh, and hath nothing in me.
John 14:31 But that the world may know that I love the Father; and as the Father gave me commandment, even so I do. Arise, let us go hence.
Study Lenses
The verse centers on "told", "before", "come", "pass", "might", and "believe". It is saying that the verse draws attention to "told" and "before", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 28's "Ye have heard how I said unto..." into verse 30's "Hereafter I will not talk much with...", so "told" and "before" 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 "told" and "before" with trust shaped by these words, not by a vague optimism outside the passage.