John 16:13

Howbeit when He, the Spirit of truth (see above xiv. 17), shall come, He will teach you all truth, which it is fitting you should know in this life, both for guiding yourselves and all nations into the way of salvation. So S. Cyril, Theophylact, Euthymius. For He would not teach them all truth in this life, but in heaven. So S. Augustine and Bede. In the Greek [as in English Version] we read " will guide you into all truth." For the way to attain truth is study, examination of Holy Scripture, the works of the Fathers, prayer and invocation of the Holy Spirit. It is therefore clear that the Holy Spirit gradually taught the Apostles more and greater mysteries. It is plain from Acts x. that long after Pentecost He revealed to S. Peter that the Gospel was to be preached to the Gentiles, and from Acts xv. that the Gentiles were not to be circumcised, or obliged to keep the law of Moses. Wherefore on the Thursday after Pentecost the Church prays, "We beseech Thee, 0 Lord, that the Comforter, who proceedeth from Thee, may enlighten our hearts, and lead them, as Thy Son promised, into all truth."

For He shall not speak of Himself, but whatsoever He shall hear, He shall speak. (1.) S. Chrysostom explains, He shall not teach anything contrary to what I have taught (so also S. Cyril, Theophylact, Rupertus, Maldonatus). S. Chrysostom says, This is added, lest by saying that the Holy Spirit would teach all truth, He should make Him greater than the Son, as though He did not teach all truth. (2.) S. Ambrose (de Spirit. Sancto, ii. 12) explains, "He shall not speak of Himself," i.e., not without participation with the Father and Myself, and therefore what He shall speak the Father and the Son will speak also. (3.) S. Augustine: "He speaks as breathed by the Father and the Son." (4.) It is best explained by joining together the last two meanings in this way: He will not speak of Himself, but by the will of the Father and Myself, for He is "of" Both. (See Didymus de Sp. S.) Christ here alludes to men who are said to speak "of themselves" when they invent anything out of their own brain, And he was a Samaritan : a Samaritan, and therefore an alien from and abhorrent to the Jews, a schismatic moreover, so that it was wonderful that he alone gave thanks so earnestly to Jesus, who was a Jew, when the other lepers, who were Jews by nation and religion, passed Him by and gave no thanks for so great a benefit.