Hi, Here is why I believe we don't need anything more that the Bible to teach us about Christ Jesus and the way of salvation..This is my belief and I speak for myself on this.
Its Origin
Inspired 2 Timothy 3: 16 All Scripture is inspired by God and profitable for teaching, for reproof, for correction and for training in righteouness...
Holy Spirit John 16:13 " But when He, the Spirit of Truth comes, He will guide you into all truth for He will not Speak on His own initiative but whatever he hears he will speak and he will disclose to you what is to come".
Holy Men 2Peter 1:21 For no prophecy was ever made by an act of Human will but Men moved by the Holy Spirit spoke from God..
With these above verses alone, I don't see anything else needed to trust that the Bible we have is the word of God..If its not then Peter must have lied.
Its Purpose
It keeps us from sin Ps 119:11 " Your word I have treasured in my heart that I may not sin against you.."
It Lights our way PS 119:105 " Your word is a lamp to my feet and a light to my path"
It purifies us..1Peter 1:22 Since you have in obedience to the truth purified your souls for a sincere love of the brethren, feverently love one another from the heart..
Free us John 8:32 And you will know the truth and the truth will make you free.
It saves us..James 1:21 Therefore putting aside all filthiness and all that remains of wickedness, in Humainity recieve the word implanted Which is able to SAVE YOUR SOULS..
Its Compleatness
ALL TRUTH..John 16:13 [ Scripture written out in previously above ]
ALL THINGS 2 peter 1:3 Seeing that HIS DIVINE power has granted us to us EVERYTHING PERTAINING TO LIFE AND GODLINESS through the TRUE KNOWLEGE of Him who called us by his own glory and excellence.
The Whole counsil Acts 20:27 2 For I did not shrink from declaring to you the WHOLE PURPOSE OF GOD...
Its indestructability
Lasts forever Mathew 24:35 Heaven and earth will pass away but my words will not pass away..
1 Peter 1:25 But the words of the Lord endure forever And this is the Word that was preached to you...
The Bible warns
Do not add or subtract from Deut 4:2 you shall not add to the word which I am commanding you , NOR take away from it, that you may keep the commandments of the Lord your God...
Proverbs 30:6 Do Not add to His words or he will reprove you and you will be proved a liar..
Rev 22: 18-19 I testify to everyone who hears the words of the prophecy of this book if anyone adds to them God will add to him the plagues which are written in this book.
Do not substitute Human Ideas Mark 7:7-9 But in vain do they worship me Teaching as Doctrines of men Neglecting the Commandment of God you hold to the tradition of men..
Preach and teach only Gods word...2Timothy 4:2 Preach the word, be ready in season and out of season, reprove, rebuke, exhort with great patience and instruction..[See also 1Peter 4:11]
Believe no other Gospel Galations 1:8 But even if we or an angel from heaven should preach to you any other Gospel contrary to what we have preached to you he is to be accursed..
His word will judge us John 12: 48 " He who rejects me and DOES NOT MY SAYINGS, has one who judges him the word I spoke is what will judge him at the last day..
The Bible answers Three questions
The origin of Life ...where did I come from
The purpose of Life..why am I hear..
After death then what...where am I going...
The Bible contains
The Mind of God
The state of man
the way of salvation
The happiness of believers
The Doom of sinners..
Well I can't answer anymore than I have already done as to why I would need anything more..Its all there...