You might notice that when God speaks in the pages of Old Testament scripture, Moses or the prophets, or their scribes, write things in the first person, and switch point of view between "the prophet" and God. The New Testament is almost entirely about what Christ has done for us or what He is doing through His church. God no longer needs to speak through anointed king or priest or prophet to make Himself known, but uses His word to introduce Himself in the person of His Son to all those who would receive Him. Even those who meet Him without the benefit of scripture, have usually heard of Him, have heard someone proclaiming the gospel, which is indeed from God's mouth to our ears. There could be no faith without hearing the word preached and no life without the breath of His Spirit received by faith in the Word made flesh, even our Lord Jesus Christ.
Some people like their god neatly tucked away on a shelf or stored away in a box, and this will always be objectionable to those who know and love Him.
My mind can always imagine God to be saying something which He hasn't said, but the Apostle points out that we have a more sure word in scripture. The written word is tested, tried, proven true. Some writings, such as from the proverbs, are not universally true, but express commonalities and conventional wisdom as generalized instruction for life. The Lord is entirely able to lead us by His Spirit alone, but since He allows us choice and desires that we choose good over evil, how should we be informed in our choices? By our own "evil" imagination?