You asked about the books that were removed to form the Protestant Bible and the significance of what they contain. Here is what your non-denominational Bible study is missing:
**Of the approximately 300 Old Testament quotes in the New Testament, approximately 2/3 of them came from the Septuagint (the Greek translation of the Old Testament) which included the deuterocanonical books that the Protestants later removed. This is additional evidence that Jesus and the apostles viewed the deuterocanonical books as part of canon of the Old Testament. Here are some examples:
Matt. 1:23 / Isaiah 7:14** - behold, a “virgin” shall conceive. Hebrew - behold, a “young woman” shall conceive.
Matt. 3:3; Mark 1:3; John 1:23 / Isaiah 40:3 - make “His paths straight.” Hebrew - make “level in the desert a highway.”
Matt. 9:13; 12:7 / Hosea 6:6 - I desire “mercy” and not sacrifice. Hebrew - I desire “goodness” and not sacrifice.
Matt. 12:21 / Isaiah 42:4 - in His name will the Gentiles hope (or trust). Hebrew - the isles shall wait for his law.
Matt. 13:15 / Isaiah 6:10 - heart grown dull; eyes have closed; to heal. Hebrew - heart is fat; ears are heavy; eyes are shut; be healed.
Matt. 15:9; Mark 7:7 / Isaiah 29:13 - teaching as doctrines the precepts of men. Hebrew - a commandment of men (not doctrines).
Matt. 21:16 / Psalm 8:2 - out of the mouth of babes and sucklings thou has “perfect praise.” Hebrew - thou has “established strength.”
Mark 7:6-8 – Jesus quotes Isaiah 29:13 from the Septuagint – “This people honors me with their lips, but their heart is far from me; in vain do they worship me, teaching as doctrines the precepts of men.”
Luke 3:5-6 / Isaiah 40:4-5 - crooked be made straight, rough ways smooth, shall see salvation. Hebrew - omits these phrases.
Luke 4:18 / Isaiah 61:1 - and recovering of sight to the blind. Hebrew - the opening of prison to them that are bound.
Luke 4:18 / Isaiah 58:6 - to set at liberty those that are oppressed (or bruised). Hebrew - to let the oppressed go free.
John 6:31 / Psalm 78:24 - He gave them “bread” out of heaven to eat. Hebrew - gave them “food” or “grain” from heaven.
John 12:38 / Isaiah 53:1 - who has believed our “report?” Hebrew - who has believed our “message?”
John 12:40 / Isaiah 6:10 - lest they should see with eyes…turn for me to heal them. Hebrew - shut their eyes…and be healed.
Acts 2:19 / Joel 2:30 - blood and fire and “vapor” of smoke. Hebrew - blood and fire and “pillars” or “columns” of smoke.
Acts 2:25-26 / Psalm 16:8 - I saw…tongue rejoiced…dwell in hope… Hebrew - I have set…glory rejoiced…dwell in safety.
There are hundreds of references in the New Testament to books in the Old Testament that you do not have access to in your Protestant Bible study. Here are more:
scripturecatholic.com/septuagint.html