The apostle Paul used the words mystery and mysteries twenty times in his thirteen inspired epistles (Romans through Philemon). Each reference is associated with the body of truth that the risen and glorified Christ personally revealed to him from heaven that he might make it known to the church which is the body of Christ. By the grace of God he preached this truth among the Gentiles and it was his burden "to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God" (Ephesians 3:9).
The mystery is a major Bible doctrine that all believers should understand and work to make known to others. Yet when is the last time that you either heard or read a Bible study on this great doctrine? There is a glaring absence of it in pulpits and Christian literature. Why is that? I think that many do not see this truth because they have not personally searched the scriptures to see whether it is so (Acts 17:11). Many others will just totally dismiss it without sincere consideration because it does not line up with their preconceived ideas and traditional (but wrong) interpretations.
The degree of light that the Lord will give us in his word depends upon what we do with the light that he has already given us. As we receive and walk in the light of God's word, he will give us more light. No one has mastered the Bible. There are deep things in it waiting to be brought to light for those who are willing to search it with a heart and mind that is wholly dependent upon the Spirit of God. Consider what Paul said in this regard:
6 Howbeit we speak wisdom among them that are perfect: yet not the wisdom of this world, nor of the princes of this world, that come to nought:
7 But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory:
8 Which none of the princes of this world knew: for had they known it, they would not have crucified the Lord of glory.
9 But as it is written, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him.
10 But God hath revealed them unto us by his Spirit: for the Spirit searcheth all things, yea, the deep things of God.
11 For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God.
12 Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given us of God.
13 Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual things with spiritual. (1 Corinthians 2:6-13)
While all scripture is certainly for us (Romans 15:4; 2 Timothy 3:16), it was not all written about us, or directly to us. God's word was given by progressive revelation. In other words, He did not reveal everything at once. As God dispensed new revelation to man, there were corresponding changes in the way that he dealt with man. God does not change in his person, principles, or promises (Hebrews 13:8), but he does change in the way that he deals with man.
For example, consider the issue of eating meat. In the beginning God told Adam that fruits and vegetables would be his meat (Genesis 1:29). About fifteen hundred years later, God told Noah that "every living thing that liveth shall be meat for you; even as the green herb have I given you all things. But flesh with the life thereof, which is the blood thereof, shall ye not eat" (Genesis 9:3-4). A thousand years after that God revealed to Moses that the children of Israel were not to eat certain meats which He called unclean (Leviticus 11). Finally, about fifteen hundred years later, God revealed through Paul that the church is free to eat any meat (even if it is cooked rare) and that those who would command us to "abstain from meats" are teaching the "doctrines of devils" (1 Timothy 4:1-5). This illustrates progressive revelation and how God changes in his dealings with man according to what he has revealed.
In the only verse in which we are commanded to study the word of God we are also told why to do it and how to do it:
Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth. (2 Timothy 2:15)
To rightly divide the word of truth is to recognize and consistently maintain the divisions that God put in the scripture. Right division does not diminish any part of the word because it is all "the word of truth." However, the mystery of the body of Christ is a distinct revelation that was made known through Paul's ministry (Ephesians 3:3), and we must consistently divide it from what was made known before him. Much of the doctrinal confusion and division that exists in the professing church is a result of the failure to rightly divide the scripture.
Five Keys to Bible Study
1. Believe the scriptures (1 Thessalonians 2:13)
2. Search the scriptures (Acts 17:11)
3. Compare scripture with scripture (1 Corinthians 2:13)
4. Consider the scriptures written by Paul (2 Timothy 2:7)
5. Rightly divide the scriptures (2 Timothy 2:15)