How can I convince someone that the Holy Book of Genesis and the rest of the Old Testament are just as important as the New Testament? What is the importance of all the measurements and numbers in the Holy Book of Genesis?
First, you need to emphasize the importance of the whole Old Testament.
The Old Testament is that part of Holy Scripture known and quoted by our Lord Jesus Himself and the New Testament writers. Often, it is viewed as the prologue to the New Testament, a document full of promises and prophesies that found fulfillment and interpretation in the New Testament and the Person, Jesus Christ.
To follow our Lord Jesus Christís teachings, we, Christians have to examine what he has taught. In all of His teachings our Lord never ignored the Old Testament, neither had the apostles nor the early church.
In referring to the Old Testament, New Testament writers use the term "Scripture." The word "Scripture(s)Ē is only found in the New Testament with the only exception in the Book of Daniel (Daniel 10:21). St. Paul instructed his disciple St. Timothy saying, "And that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus. All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness" (2 Timothy 3:15-16).The "Scripture" that St. Timothy had known since he was a child could not be the New Testament writings; for during that time, the bulk of what we now call New Testament had not been written, or if some were, they were only in the form of letters.
The "Scriptures" that St. Paul is referring to are obviously the Old Testament, as we know it. It was the only complete Divine writings in their possession during their lifetime. This Old Testament can make us wise for salvation as St. Paul taught.
St. Paul's teachings were verified by these "Scriptures". "These were more fair-minded than those in Thessalonica, in that they received the word with all readiness, and searched the Scriptures daily to find out whether these things were so" (Acts 17:11).
Our Lord Jesus Christ Himself attested that the Old Testament contains words that will lead to eternal life "You search the Scriptures, for in them you think you have eternal life; and these are they which testify of Me" (John 5:39). It is for this reason that He plainly stated that the entire Old Testament talks about Him (Luke 24:27). Our Lord did testify that He will magnify the Old Testament teachings and writings, "Then He said to them, "These are the words which I spoke to you while I was still with you, that all things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me." (Luke 24:44). Now the word "fulfill" is the Greek pleroo, which means, "to make it full" or "magnify and make it honorable." It has nothing to do with revoke! Isaiah the prophet wrote that the Messiah's intention is to magnify the laws of God, to bring it back to its fullest and right intent as God had originally framed it (Isaiah 42:21). This is the example that our Lord Jesus has set for true Christians to follow by keeping His Father's commandments and laws (John 14:15; John 15:10). He has no intent to abolish these laws but to "fulfill" (pleroo) them. He even made this clear in the Sermon on the Mount (Matthew 5:17).
In the Holy Book of Revelation, there are over five hundred and fifty Old Testament references to the end of time. This only reinforces what St. Paul had taught that the lessons from the events in the Old Testament are very important for the end-time generation (I Corinthians 10:11). We really must take our Lord and His faithful apostles as our model in teaching studying, and reading the Holy Bible (I Corinthians 11:1). Jesus is consistent all the time (Hebrews 13:8).
The message of the New Testament is scattered all over the Old Testament; without the Old Testament, it would be almost impossible to get the entire picture of God's salvation plan.
Secondly, discuss the importance of the Holy Book of Genesis. The main emphasis of this book is the preparation for salvation. It starts with the creation and the fall of man. It introduces the history of salvation, then through the Patriarchs prepares to announce the Incarnation of the Savior. It contains many symbols of Christ such as the Tree of Life (Gen 3:22); the ark (1 Pet 3:20, 21); Melchizedek (14:18-20) etc.
Thirdly, it is true there are many numbers mentioned in the Holy book of Genesis mostly the ages of Adamís descendants, as well as measurements. However, some of these numbers can be looked upon in a symbolic way. For instance, the measurement of Noah's ark, its length was 300 cubits. The number 100 represents Christ's flock (Luke 15:4-5) that was sanctified by their belief in the Trinity (100 x 3). Its width was 50 cubits. The number 50 represents the enjoyment of forgiveness from sin and liberation (Jubilee) by the Holy Spirit (Pentecost), the Spirit of Love. Its height was 30 cubits. The number 30 reminds us of Joseph who left prison for the palace at the age of 30, as if from earth to heaven. It reminds us also of the age of our Lord Incarnate when He began His public ministry on earth.
To benefit more from reading the Holy Bible, I recommend reading it with a commentary. You can check these websites for an introduction to the Holy Book of Genesis by Fr. Tadros Malaty http://www.st-peter-st-paul-coptic-orthodox-church.org/Genesis.htm