John 17:20

Neither for these only do I pray, but for them also that believe on me through their word.

Here the prayer reached out toward the saved of all generations. Significantly, all who would believe on Jesus would do so "through their word," that is, through the word of the apostles, there being no other way that faith can be produced. Such being the case for conversion, why should it be thought strange that the work of the Holy Spirit in the hearts of believers, after they are converted, should follow exactly the same pattern?

Through their word ... is not a merely incidental thought. Peter wrote: "Remember the words which were spoken before by the holy prophets, and the commandment of the Lord and Saviour through your apostles" (2 Peter 3:2). These words are equivalent to saying that there is no other way of bringing men to God except through the word of the apostles.