Jesus says that previously He taught them in short, traditional sayings, which expressed obvious truths. A time is coming when various teachings will be spoken plainly. In the Old Testament, proverbs and riddles were used to teach various topics. Although the disciples are not ready for the full understanding of the new relationship with God that Jesus describes, He is getting them ready. http://ref.ly/Jn16.12
As stated earlier, they will have the privilege of praying in His name, and their prayers will be answered. Their new relationship will cause them to know the love of the Father. They believe that Jesus came from the Father. Jesus lets them know He is returning to His place with the Father.
In response to these facts, the disciples tell Jesus that He is now speaking plainly. They now understand His teachings. They say that they know that Jesus has all knowledge. That is why He has no need for them to ask Him any questions because of He has special insight. Note http://ref.ly/Jn1.42 and http://ref.ly/Jn2.24f.
Notice that there is a transition from verse 29 to verse 30. The word used is “now.” There is a time coming when they will be scattered because Jesus is leaving. Note that this may refer to Zech. 13:7 (compare this verse with Matthew 26:31). The Old Testament often says that God’s flock will be scattered for lack of a good shepherd. Compare this statement with Isaiah 53:6; Jeremiah 23:1 and Ezekiel 34:6. Jesus will be left alone. Yet He is not alone because the Father is with Him.