This Gospel (John 14:23-31) is a part of the exhortation which Christ addressed to His disciples on the evening before His sufferings, and contains words of especial importance. Christ would teach us in these words how vain is the endeavor to obtain a knowledge of God and to come to Him without loving: the Saviour. Where this is wanting, our thoughts of God and our devotion are without assurance and we cannot apprehend Him. But if we love Christ we can come to the Father and He will love us.  How is it that Christ here speaks of love and does not say, as He is wont to say: “Believe in me?” Is love more efficacious than faith that He says: “If a man loves me?” We answer: The sense is the same; man cannot truly love Christ unless he believes in Him and is comforted in Him. The word “love” is in this case plainer and more forcible, because it indicates so nicely, how our hearts should turn from everything else in heaven and on earth, and should cling alone to this Man, Jesus Christ. For we know how love, according to its
very nature, concentrates all its energies upon the object of its devotion, and remains attached to it, regardless of aught else in the wide world. It is the Lord’s will that we should thus cherish and love Him with our whole heart. This we cannot do except through faith. Hence this declaration concerning love does not in the least detract anything from faith, but rather instructs us as to the true character and efficacy of faith. (Luther’s House Postil, Second Sermon for Pentecost, Volume 2, p. 598-599)

What is the consolation which the Holy Spirit brings? “He shall testify of me.” says the Lord; that is: The devil will surely terrify and the world will persecute and kill the Christians, but the Holy Spirit will be present with His testimony to arouse faith and to encourage the wavering heart, making it firm in Christ. The Comforter will indeed not bring us thousands of dollars in our distress, as perhaps the world would do, but He will cheer us with the Gospel and the word of promise, so that we can exclaim: Let them take all, family and home, our goods and our honor, yea, even our life, yet we will not despond, for we have a Helper above, Christ Jesus our Lord, who for us became man, and died and arose again from the dead, and ascended into heaven in our behalf, as we daily confess in our Creed. Why then should we fear? The Son of God, our Lord, who went into death for us, cannot be our enemy, but will defend and aid us under all circumstances. If He thus loves us, then surely have we no cause whatever to fear or to mistrust Him. This consolation we find in the words of Christ: “He shall testify of me,” for outside of this testimony of the Holy Spirit concerning Christ there is no sure and abiding consolation. The words “of me” ought therefore to be written in large letters and well remembered. They teach us that the Holy Spirit, when He comes to console, preaches no other doctrine, not the law, nor anything else but Christ, since it is impossible to comfort the troubled hearts except by preaching Christ’s death and resurrection. It is certain that the urging of the law, of good works and an unblemished life, brings no consolation; it only makes men
diffident and full of fear; for without Christ God appears terrible, full of wrath and ready to punish. The preaching of Christ alone conveys true consolation, which beyond all doubt makes glad the hearts and cheers them in all sorrow. (Luther’s House Postil, Sunday after Ascension, Volume 2, p. 581-582)