Everyone divides the word of God to some extent. If you don't believe that we need to perform animal sacrifices today, administered by the priestly order from the tribe of Levi, you are recognizing a basic division in God's word. What you are saying is that you do not believe it appropriate or honest to apply to yourself during this present time those commandments and instructions given to Israel about the animal sacrifices. For, you recognize that those instructions were given to a different audience, at a different time, and are not given to you today. That is dividing God's word. And it is very appropriate and necessary to divide the word for it covers all of the history of our world, from beginning to end, and we are only living in a fraction of that history. Surely God had different instructions at different times for his people.
As II Timothy 2:15 clearly states, Bible handlers must "study to shew thyself approved unto God...rightly dividing the word of truth." If we are to divide God's word correctly and accurately, thus "rightly divide" it, we must learn from God where to make divisions in His word. We do that by identifying where God is speaking directly to and about us today, and where He is not speaking to and about us today.
We recognize a basic three-fold division of God's word: time past, but now, and ages to come (Ephesians 2).
"Time past" refers to God's dealing with his nation Israel to the exclusion of the Gentiles. This period covers Israel's creation in Genesis 12 through the Old Testament, continuing through the gospel accounts and the preaching of Christ as the risen Messiah of Israel in Acts 1–7.
"But now" is a designation that refers to this present time in which we live called the "dispensation of grace." The "but now" age began in Acts 9 when God interrupted His program with Israel to accomplish another purpose prior to His day of wrath. This other purpose God had always planned, yet had previously never spoken about. Unexpectedly, therefore, God raised up a new apostle, different from the 12, the Apostle Paul, and sent him to "the Gentiles, and kings, and the children of Israel..." preaching the gospel of Christ "according to the revelation of the mystery, which was kept secret since the world began." Therefore, Paul is called the "apostle of the Gentiles" and is used uniquely by God to reveal the grand mercy and grace God is offering every person on earth, Jew or Gentile, and what is God's plan and purpose for the church today. God used Paul to record these things in the epistles of Romans–Philemon, the portion of God's word written to and about us today.
Ages to Come
"Ages to come" refers to the time that will immediately follow this present time, wherein God will resume his program with Israel and complete it. The Day of the Lord's wrath will come, followed by the 1000 year reign of Christ on earth. Ultimately God will unite all things under the headship of Christ Jesus our Lord, both which are in heaven and in earth.
For a visual representation of God's three-fold division to His word, see Enjoy the Bible's timeline of God's word. There you will find other helpful material about studying God's word rightly divided.