In the beginning and throughout the Patriarchal dispensation, with very few exceptions, God spoke directly to the original heads of households. When we say directly, this includes via visions and dreams as well as speaking directly to them. Yet, He did not speak directly to every person, and it is apparent that he did not speak to the head of each household. The mere fact that so many completely abandoned the true God seems to be evidence that God's word was not passed on from the early patriarchs as it must have been intended. We know that God spoke directly to Noah in whom He had found faithfulness. And through Noah we have record that God chose to have him preach to the people for the 120 years while he was building the ark. So this is one of the few times that we have that God spoke to the people via some human during this dispensation.
Then we have instances of evidence where others may have also taught. We learn that there were priests during that dispensation in Genesis 14:18 in the person of Melchizedek, the king of Salem. And it is likely these priests had a responsibility of teaching.
Of course, we also know that God spoke directly to Abraham and others during this time.
When the seed of Abraham via Isaac and Jacob, brought into being the 12 tribes of Israel (Jacob's name was changed to Israel), God continued to speak directly to Moses and worked miracles also through Moses and following Moses, Joshua, until the tribes had settled in the land of Canaan. After Joshua, the tribes were left on their own for the most part and as man has always done, they strayed from God. As they left following after God, He would allow their enemies to give them difficulties and other things such as failing crops, etc., and when they came to their senses and prayed to God for help, He raised up, a hero, a judge to lead them from their problems, and lead them back into worshipping God. This scenario occurred over and over until the time of
Samuel, who was their last judge. While Samuel was judge, the people began to cry out that they wanted a king, like the nations around them. Although Samuel tried to discourage them, they continued until God had Samuel to anoint them a king.
The king then ruled the people and God spoke to the kings. After the kings, Saul, David and Solomon, the kingdom divided. After they formed a northern kingdom, which retained the name Israel, and the southern kingdom which became Judah, they had their separate kings but for the most part they were ungodly kings who led their nations into idolatry. Israel, never had a king which attempted to follow God's directives, while the southern kingdom, Judah had perhaps three which could be termed good kings.
During this period of the divided kingdom, God raised up prophets to warn and instruct the people concerning His will. Many of the books of the Old Testament are those very prophets which showed God's love for the Jewish nation and His desire to have them obey Him.
Then came the advent of the Christian age. Jesus was born, lived and died under the Old Testament Law, in order to bring salvation into the reach of all men of every nation and race. Here are some scriptures which describe the means of communication between God and man, both before and after the Christian era began. The first one is very meaningful and easily understood.
"God, who at various times and in various ways spoke in time past to the fathers by the prophets, has in these last days spoken to us by His Son, whom He has appointed heir of all things, through whom also He made the worlds; who being the brightness of His glory and the express image of His person, and upholding all things by the word of His power, when He had by Himself purged our sins, sat down at the right hand of the Majesty on high." (Hebrews 1:1-3 KJV)
This passage describes what we have attempted to present above as to the communication 'in time past' referring to the Old Testament. Then it explains that Jesus is our source of information throughout the remainder of time. It does not give the details as to how we receive if from Jesus but we have that explained elsewhere. Read this carefully:
"Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you. And when he is come, he will reprove the world of sin, and of righteousness, and of judgment: Of sin, because they believe not on me; Of righteousness, because I go to my Father, and ye see me no more; Of judgment, because the prince of this world is judged. I have yet many things to say unto you, but ye cannot bear them now. Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come. He shall glorify me: for he shall receive of mine, and shall shew it unto you. All things that the Father hath are mine: therefore said I, that he shall take of mine, and shall shew it unto you.' (John 16:7-15 KJV)
Notice that the Holy Spirit, "shall not speak of himself but whatsoever he shall hear, that shall he speak:" plus, "for he shall receive of mine, and shall shew it unto you". In other words, he will put into the apostles minds the very things Jesus says, and therefore, whatever they say, or write is the words from Jesus himself. What we read from the New Testament are the very things Jesus has said to the apostles and what he instructed the Holy Spirit to say to them. I matters not that it is written by the pen of an apostle, it is the word of Jesus Christ.
There are other scriptures which show that the Christians is to no longer observe the laws given to man before Jesus Christ. Read this:
"And, behold, there appeared unto them Moses and Elias talking with him. Then answered Peter, and said unto Jesus, Lord, it is good for us to be here: if thou wilt, let us make here three tabernacles; one for thee, and one for Moses, and one for Elias. While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him." (Matthew 17:3-5 KJV)
This event occurred on the mount of transfiguration. Jesus was glorified and Moses and Elias appear to them. Moses and Elias were considered the most highly influential characters under the Old Testament Law and the most difficult for the Jewish converts to Christ, to forsake. But God uses this occasion to explain to them in His brief statement, who they were to follow from henceforth. In our modern English language the last phrase would have been something similar to this: "...you listen to him!" Which also means that Jesus is our only source of salvation and the past has nothing to do with it.
There are certain writers in the New Testament which were not apostles, however, these were given the gift of evangelism via the Holy Spirit as were the apostles. This was done by the power vested in the apostles to lay their hands upon a newly baptized Christian and bestow the gift of the Holy Spirit. Luke is one who was very close to the apostle Paul and who wrote the Gospel according to Luke and also the Book of Acts. John Mark is another, the author of the Gospel according to Mark, who was a cousin to Barnabas and he ministered to Paul and Peter in their older age. Jude also was not an apostle but is said to have been the half brother and brother to James. The gospel of James also is thought to have been written by the half brother of Jesus rather than one of the apostles.
All the writers were inspired of God by the Holy Spirit and the words are those of Jesus. Hear ye him!