John 16:26

At that day,

the day when they were baptized with the Holy Spirit, Pentecost, and from that time on,

ye shall ask in my name.

This fulness of knowledge is connected with fulness of prayer. For days before the descent of the Holy Spirit "the apostles, disciples and brethren of the Lord, continued with one accord in prayer, with the women." The apostolic church founded on Pentecost "continued steadfastly in the apostles' teaching, and the fellowship, and the breaking of bread and prayers." Those filled with the Holy Spirit engage in bolder petitions in Christ's name.

I say not.. that. will pray the Father for you.

Their relation to the Father, who "has sent his Spirit into their hearts because they are sons," making them temples of God in which the Father dwells, as well as the Son, is so intimate that they may approach him themselves, and he does not need to say that he will pray the Father for them.