It is written in the prophets, "They will all be taught by God." Everyone who listens to the Father and learns from him comes to me.
This is a quote from Isaiah 54:13 but it is a typical promise of the later prophets and indeed of Jesus' time on earth. Thus Jeremiah looks forward to a new covenant written on men's hearts (31:31-4); a new heart and spirit is promised in Ezekiel (36:24-6); and Joel promises God's spirit poured out on all peoples (2:28ff). John announces the fulfilment of these prophesies in the language of being born again and in the farewell address of John 14 he emphasises the teaching role of the Holy Spirit and in his first epistle the anointing role.
The coming of the Holy Spirit is about to make devastating changes in the life of a Christian; it will never be the same again.