These are the last words of Christ to the public and they are His last appeal to believe. John places them here to summarize everything that has gone before, but they were probably said immediately before verse (12:36).

John 12:36  Put your trust in the light while you have it, so that you may become sons of light.” When he had finished speaking, Jesus left and hid himself from them.

“cried out” = Jesus spoke these words loudly, probably because of their importance. This is a nice contrast to those leaders who believed in Him but were too frightened to speak of their beliefs in public.

Jesus and the Father are so close that to believe in One is to believe in the Other.