Since “expedient” means advantageous, the Lord was saying it was to their advantage if He left, for that meant the Spirit would come (v.7). He said this to console them since they were sorrowing that He was leaving (v.6).
But how would losing Him and gaining the Spirit be an advantage? It was because the Spirit was “the Spirit of truth” (14:17), and Christ was “the truth” (14:6 cf. I Pe.1:11). So the Spirit dwelt “with” them in Christ, but would be in them at Pentecost (John 14:17). This is an advantage, despite how Christians who have the Spirit in them wish they could have been there with Him. It may not feel like an advantage, but trust the Lord’s words over your feelings! And if you want to hear His words, pick up a Bible. If you want to hug Him, hug a member of His Body!
The Lord’s coming would not be expedient for the world, whom He would reprove for three things (John 16:8). Reprove means to blame someone or charge them with a fault, and that’s how the Greek word for reprove is translated in Matthew 18:15.
The Spirit reproved the world of sin (16:9) because Christ came to take away their sin, but rather than accepting Him they killed Him. So at Pentecost the Spirit blamed them for this through a man filled with the Spirit (Acts 2:22; 3:13-15). Christ came to give righteousness to the world (Dan.9: 24), so when the world rejected Him and His offer of righteousness the Spirit reproved them for this (John 16:10)
Christ came to set up a kingdom in which He would judge the world (Jer.33:15), even the poor (Isa. 11:1-6). He would “judge” the poor in the I Corinthians 6:3 sense of reigning over them. Sin will be judged with death in the kingdom (Isa.65:20), but if you say a property is yours and your neighbor says it is his, this matter needs a judgment. When the world rejected the Lord’s judgment, the Spirit came to reprove them “of judgment” (John 16:11), especially since “the prince of this world is judged.” He’s the current ruler of this world. When Adam sinned, Satan claimed the property of the world was his, and God agreed. But Christ paid for the right to rule the earth with His blood and received the deed to the earth in when God agreed the property was His (Rv.5:1-10). They deserved to be reproved for rejecting Christ as their ruler once Satan was judged and stripped of his right to rule the world (Col.2:15)
The 12 couldn’t bear the things the Lord wanted to tell them (John 16:12) because they were babes (cf. ICor.3:1,2), so He was always careful what He told them (Mark 4:33). But right before the kingdom they were to become sons (Hosea 1:10,11), and this began at Pentecost (IJo.3:2). What made the difference? They went from babes to men because the Spirit indwelt them (Acts 2:4). That’s why the Lord told them that they couldn’t bear the things at that time, but could when the Spirit came (John 16:13).
The Lord said the Spirit would guide them into all truth (16:13) and He did (I John 2:20,27). When the Lord said He would “not speak of Himself,” that didn’t mean He wouldn’t talk about Himself, it meant He wouldn’t speak His own words (cf. John 12:49), but the Lord’s words. That’s why the Lord went on to say that He would speak “whatsoever He shall hear” (John 16:13 cf. 14:26). That’s what the Spirit always does, remind you of God’s Word.
But the Spirit would have to do more than just remind them of what they heard from Christ, for He had just said there were things He couldn’t tell them because they couldn’t bear them. So the Lord went on to say that the Spirit would “shew you things to come” (John 16:13), and He did (Acts 2:18 cf. Heb.9:11; 10:1; 13:14). But if the things to come were good, why couldn’t the 12 bear them at that time? Not all the things to come were good! The book of Revela-tion is a “prophecy” of terrible things to come (Rev.1:1-3). The 12, who all ran when the Lord was arrested, could not have borne to hear about those things at that time.
So the Lord said the Spirit would receive His words and give them to the 12 (John 16:14,15 cf. Mt.11:25-27). This would glorify the Lord (16:14). It always glorifies the Lord when we take His words and give them to others!