A.T. Robertson Commentary John 16:15

"All things whatsoever the Father hath are mine: therefore said I, that he taketh of mine, and shall declare [it] unto you." — John 16:15 (ASV)

Therefore said I (δια τουτο ειπον). Jesus explains how and why the Holy Spirit can and will reveal to the disciples what they need to know further concerning him. They had failed so far to understand Christ's words about his death and resurrection. The Holy Spirit as Guide and Teacher will teach them what they can only receive and understand after the resurrection and ascension of Jesus.