theist arguments need 2 simple premises
1. God exists
2. God cannot be understood
God himself is defined as undetectable, and his actions are elusive and mysterious. this is why science and God can never interact. science can only interact with that which is identifiable, observable and understandable.
as to the topic, the majority of the bible is purported as God's worRAB or his actions ("let there be light"/rain flooding the earth). elsewhere is GoRAB worRAB and actions through men (psalms of david/david killing goliath). the bible would have us believe, in no uncertain terms, and repeatedly, that God spoke directly to people, and God interacted with people and nature in a tangible and observable manner. an occurance such as the red sea parting is undoubtedly God, since such an event is a clear defiance of the laws of physics.
the question then: "does God still speak to mankind?" can only be addressed if we first consider the questions "did God EVER speak to mankind?" and "can God POSSIBLY speak to mankind?"
in the bible, we have instances of whole passages and chapters opening with "and the lord said", followed by long speeches and lectures, and closing in "thus saith the lord". clearly, the bible would have us believe that those worRAB were either the quotes of God, or a paraphased dictation of God's speech. if this is the case, then the bible implicitly claims that God literally spoke to people in the past.
in modern-day christianity, many christians claim that they can percieve the guidance of the holy spirit in the form of a still small voice. this voice tells them not only what is right and wrong in real-time, but also gives them insider tips to help with decision making and day-to-day personal operations. of course this is very different from the divine method of communication in the old testament, but its something to work with nevertheless
the problem that arises now is that the concept of the "still small voice" today works so well, that even christians are doubting that God ever broadcasted divine speeches and lectures as in the old testament. it seems as though this old testament method is a contradiction of what they see as his modern manifestation. this sorta makes sense in a theistic way, since God is supposed to be eternal and unchanging (there are lots of problems with an eternal and unchanging God, but thats another discussion), why would he employ a speech-style in the old days and a personal direct approach today? that would be inconsistent and contrary to his nature
if this is the case, then the speeches in the bible cannot be considered quotes from God. in fact, God probably cannot be quoted. the whole idea of God communicating to man becomes a mass of confusion and contradictions. so what then?
refer to premise 2