What does John 16:23 mean?
Despite the fears and doubts of the disciples (John 16:6, 12), Jesus has predicted that their sorrow will eventually lead to joy (John 16:20–22). In particular, this means the change these men will experience when they see Jesus alive and resurrected several days from now (John 20:19).A common theme of Jesus' earthly ministry was fielding questions from His closest followers. Much of what Jesus had to teach them would not make sense until after His resurrection (John 2:22; 6:60). They also did not yet have the influence of the Holy Spirit (John 16:13). So, in response to His comments and parables, they often posed questions (John 13:6; 14:5; 14:22; 16:19). At times, their reaction to Christ's ministry was open disagreement (Matthew 16:21–23; John 13:36–38). So long as Jesus was there, in person, they could direct those concerns directly to Him.
When Jesus is raised from the dead (Mark 8:31), however, many of these questions will be answered. At that time, the issues which frustrate the disciples will be clear. As a result, they will "ask nothing of" Jesus. What Christ says in the next verses makes it clear this statement is not about prayer requests or material needs (John 16:26). It's an additional promise that what seems blurry or obscure, for now, will soon be gloriously obvious (John 15:26–27).
Jesus also echoes the promise He gave earlier in this discourse: that requests offered in prayer, "in [His] name," would be granted by God (John 14:13–14). The context for those answers is explicitly given—to ask something "in the name of Jesus" means to invoke His authority and His will. That means any request contrary to His will has no hope of being granted. Submission to God and obedience to His Son are the key elements in this promise—not a blanket promise to give us whatever we want.
The ending promise of this verse includes a repetition of the word amēn. This has remained almost unchanged from Aramaic through Greek and into English. Leading a statement with this term, and especially by repeating it, is a claim to first-hand knowledge of infallible truth.