It is important to understand how God chose to reveal Himself if we are going to understand prophecy. To quote Charles Hodge "The progressive character of divine revelation is recognized in relation to all the great doctrines of the Bible. One of the strongest arguments for the divine origin of the Scriptures is the organic relation of its several parts." In other words it is very important to understand that God revealed Himself progressively, and not all at once. This may seem fairly obvious by looking at the diverse authorship of the books of the Bible, and the many years that God's truth took to be written down, but the understanding of progressive revelation is important in relation to prophecy. The fact that the Millennial Kingdom is to be 1000 years isn't revealed until the 3rd to the last chapter of the Bible. That doesn't make it any less true.
Probably the best example of progressive revelation in the Bible is the doctrine of the trinity. The Old Testament only alluded to this truth, but the New Testament explains it more fully. In Genesis when God said "Let us make man in our image", He doesn't go on to explain why He would speak as if to Himself in this way, but it is evident that He is speaking with Himself as if there were more than one person there. We know that He wasn't speaking with angels or any pre-existent beings, as some would say, because Genesis goes on to say in 1:27 "And God created man in His own image, in the image of God He created him; male and female He created them." He went out of His way to tell the reader that man was created specifically in the image of God, and not God and someone else. After all, no being is equal with God, and therefore could not share in God's statement.
So at this point there is somewhat of a question mark about how much one could know about the person of God. Not everything about His person was revealed. The revelation about the person of God continues over time through references to 'the Angel of the Lord'. Many times deity is assigned to this angel. The Psalms begin to make this clear as well. Psalm 45:6 says "Thy throne O God, is forever and ever; A scepter of uprightness is the scepter of Thy kingdom. Thou hast loved righteousness, and hated wickedness; Therefore God, Thy God, has anointed Thee." Hebrews 1:8 tells us that this was God the Father speaking to God the Son. The complete understanding of the triune God is spelled out in the New Testament. It seems that Jesus had to explain this for years to His disciples. They couldn't seem to grasp it, and I'm not sure they did grasp it until after the resurrection. We have more revelation then they did after the resurrection since the Apostle Paul under the inspiration of the Holy Spirit tells us in Colossians 1:15 that Jesus "...is the image of the invisible God." What better way could there be to describe a being that is equal with God than to call one the image of the other. Of course He was speaking of the second person of the trinity, who became a man, Jesus.. No person or angel can be called the image of the invisible God, or as it says in Hebrews 1:3 "the radiance of His glory, and the exact representation of his nature". God is so far above His creation that only a very small view of God can allow for a lesser created being to be said to be the image of the invisible God.
Colossians 1:16 tells us that Jesus created all things, everywhere, in heaven and earth. Interestingly it also says this... "all things have been created by Him and for Him" You have to jump through a lot of hoops to not see the uniqueness of Jesus here.
Hebrews 1:1 says this... "God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world."
You see, now we know that God the Father, Yahweh, made the world through Yahweh His Son. They are distinct persons in the Godhead, and yet one, as is the Holy Spirit. Now we have the full revelation about the person of God, but obviously during the OT times they didn't have as much revelation as we do now. It's nice to know that God held them responsible for the revelation that they had, and not what they did not have. I'm sure that there is yet more to know about God that we just can't understand in our current state.
Some might wonder whether people that don't accept Jesus Christ as Messiah will be held responsible by God. The Bible answers this question in Romans chapter 1. Listen to what God says in Romans 1:18
"For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness, because that which is known about God is evident within them: for God made it evident to them. For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse."
Before the time of Jesus Christ God held man responsible for knowing Him (through creation) and seeking Him. However, the Bible explains to us that man doesn't seek after God, even though God has revealed Himself in creation. Instead, man covers over any thoughts of God, preferring to go with one of the various scientific theories. There may have been a big bang, but it was the intelligent, personal God, creator of time and space that caused it by an act of His will.
As we explain in the section on Dispensationalism, God worked in different ways during different ages, requiring different things from man, based on the amount of revelation that man had at that time. Now that Jesus Christ His Son has been revealed, man is responsible to believe in His Son. Of course the plan of salvation has never changed. It has always been faith in God through His revealed truth. Where more revelation comes, more responsibility comes. This subject is actually intertwined with Dispensationalism, since we see the work of God inseparable from the revelation of God. Take a look at Acts 4:12:
And there is salvation in no one else; for there is no other name under heaven that has been given among men, by which we must be saved.
Definitely. According to the book of Genesis, and the book of Romans, Abraham was justified by faith, and he was called righteous. How did he become righteous? Was it by doing good? It wasn't by doing, but by believing God. There was obedience where there was true belief, so we're not saying that salvation was by mere profession. Was it by keeping the Jewish laws handed down to Moses? How could it be? Moses wasn't born yet.
Here it is: God counted true belief in Him as righteousness. He could do that because He knew Jesus would die for the sins of mankind. Abraham showed his faith by putting God before even his own son. He accepted God as the King of his life. This faith is what saved him, and not the good works that he did. He responded to God in willing obedience, and that obedience showed his faith.
God makes the rules, we don't. If God decides that the correct response to Him is faith, then that's what it is. We can't go to God and tell Him that we would rather try to earn His love through good works.