(Vs. 16) Christ speaks as mediator and promises to intercede for them (Luke 22:32; I Tim. 2:5; Rom. 8:34). Here is another reference to the trinity of persons in the Godhead--the Father prayed unto, the Son in human nature praying, and the Holy Spirit prayed for. The "Comforter" is the Holy Spirit, Who takes the things of Christ and reveals them to His people (John 16:13-14). He regenerates, sheds abroad God's love in the heart, teaches, guides, is the Spirit of adoption, seals the believer, and abides with us always as the pledge or earnest of our future glory.
(Vs. 17) He is called "the Spirit of truth" because He IS TRUTH (I John 5:6), He guides men into all truth (John 16:13), and He revealed all the truth contained in the Scriptures (Acts 1:16; II Peter 1:21). The world of natural men cannot receive the Holy Spirit nor the truth of the gospel revealed by the Holy Spirit because their eyes are blind, their ears are deaf, and they have no heart understanding of God (Matt. 13:13-16; I Cor. 2:9-14). As a result of the fall, all men are spiritually dead (Rom. 5:12; Eph. 2:1, 5) and must be regenerated or born again to see (understand) the kingdom of God (John 3:3-8), to know and love God, and to partake of eternal life. The believer knows God, he knows the Redeemer (John 17:3), and he knows the Spirit of God, Who dwells with him and in him.
(Vs. 18) "I will not leave you orphans," as when a father dies and his children are left orphans for others to care for and to raise. "I will come to you." The reference here is not to the return of Christ but to the presence of His Spirit with them, for to have the Spirit of Christ is to have Christ and the Father (Rom. 8:9: I Cor. 2:12). Our Lord ascended to heaven; but when the Holy Spirit came upon them, Christ truly returned to them (Acts 1:4-5, 8).
(Vs. 19) The world saw the man Jesus Christ with fleshly eyes. They never really saw Him nor knew Him. Soon He would be crucified, buried, risen, and exalted to the right hand of God. The world then would see Him no more in any revelation. But the believer sees Christ! Some saw Him in the flesh before He died and again after He arose. But this "seeing Christ" is with eyes of faith – Christ eternal, Christ incarnate, Christ our righteousness, Christ our redemption, Christ our mediator, and Christ our Lord. We (who never saw Him in the flesh) see Him in the Scriptures. Because He lives as God (the giver of life) and as our Redeemer (the purchaser of eternal life), we shall also live and never die. Christ is our life (Col. 3:4); and being one with Him, we shall live eternally.
(Vs. 20) When the Holy Spirit comes upon you, you will recognize and understand this spiritual union between the believer and the Lord God. "I am in the Father, you are in Me, lam in you, and we are all one" (John 17:21-23). Christ, by His Spirit, actually lives in the believer (Gal. 2:20). He is the head and we are the body. He is the vine and we are branches. To harm a believer is to harm Christ, and to bless a believer is to bless Christ (Acts 9:4; Matt. 25:40).
(Vs. 21) The believer who has the precepts and commandments of Christ has them not in a book, but written on his mind to think upon them, and on his heart to love them. By the grace of God and the power of the Spirit, he keeps them. His commandments are not grievous to those who love Him. "He it is that loveth Me." Others may talk of loving and believing on Christ, but one cannot separate faith and conduct. "As a man thinketh in his heart, so is he!" Obedience to Christ is evidence of love for Christ. Our love for Christ is not the cause or condition of the Father's love to His people, for "we love Him because He first loved us" (I John 4:10). "He that loveth Me will have A CLEARER DISCOVERY of the Father's love for him and of My love for him and I will MORE AND MORE MANIFEST Myself to him." Everything that we are and have spiritually in union with Christ is capable of growth as He is pleased to reveal Himself and His word to us (I Peter 2:1-3; II Peter 3:18; II Peter 1:4-8). So our Lord is saying that those who have seen Him and love Him, He will all their lives favor them with His presence and manifestations of His fullness, His grace, and His glory.