Roger Nicole raises some very interesting points about the relationship between the so-called "Old" and New Testaments. Specifically:

Eugen Huehn indicates 4105 passages reminiscent of Old Testament Scripture.

Given fewer than 8000 verses in the N.T., and assuming a "passage" is akin to a "verse", this means about half of the N.T. is not new.

In my personal study time, I've been reviewing N.T. doctrines and checking to see if they're represented in the Tenakh (a Hebrew acronym that means Law, Prophets, and Writings--the "Old" Testament). I have found very few doctrines unique to the N.T. The Rapture is one such doctrine. Quantifying the Kingdom at 1000 years seems unique to the B'rit Hadashah (New Covenant).

Among those doctrines Christians mistake as unique to the N.T. but are actually in the Tenakh:

• Love your enemies (Exodus 23:4-5, Proverbs 25:21-22).
• The Tribulation (Jeremiah 30:7). The Time Of Jacob's Trouble is well known to be the Tenakh's name for The Tribulation.
• God's Triune nature (read Genesis and much more). There were times the Lord Himself showed up and spoke face-to-face with His people (e.g., Abraham). There were times when not just any angel but The Angel of the Lord appeared. These are seemingly preincarnate appearances of the physical manifestation of the Lord, that is, Jesus. Countless passages speak of the Spirit of the Lord; in particular, the Spirit often inhabited God's prophets, judges, or kings. And in Genesis 1:1, the name Elohim is plural while the verb is singular, suggesting a kind of plurality to the Lord's nature while being but One.
• Salvation by faith alone, legalism is wrong (read Isaiah). Nowhere in the Tenakh does God teach legalism (despite Israel's sinful practice of it), yet this straw man is repeatedly built up and torn back down by those desiring to erase the Tenakh from the Scriptures.

At the time the N.T. was written, only the Tenakh was deemed Divinely inspired. Only the Tenakh was Scripture, and it was deemed sufficient. (This is not to say the N.T. does not have great value or that it is in any way uninspired.) When Paul exhorted Timothy to remain in the Scriptures--2 Timothy 3:14-17--he was referring to the Tenakh. When Jesus quoted and asserted the authority of Scriptures, He was referring to the Tenakh. Do not forsake this majority of God's Word.