"Sola scriptura ("by Scripture alone")" [ one of the five foundations of the reformation.]
"The letter kills , but the Spirit gives Life!" Dogma is hateful, ever so hateful, and all in chains to it's cruel mandates, justify all by scripture. Because the scripture does contain the directional image of the living Word, it can be sold, bent to ones own interpretation of it, as a means of a living faith, and mostly as THE ONE AND ONLY TRUE FAITH!
The Bible, however, is only the Bible, when the Spirit and the Word agree in revelation of it's true intent. Herein lies the rub. Many, many cults and aberrations in the church of God have been formed out of this error; exalting Scripture as a means of attaining God, without realizing that without the Spirit of God, YOU ARE NONE OF HIS! NADA!
Let me make a wild stab at the character of this person of which you speak; he or she is self willed, and granite hard in their convictions, and uses the Word of God as they understand it to condemn others every-time, therefore justifying themselves, and sees themselves as superior in their stand, and thereby others as wrong, and somewhat inferior.
They are Bible-Thumpers in their witness....am I getting close?
The Holy Spirit will always break us, and humiliate us as we become aware of our unlovliness and corruption, to repent, while The Letter will always exalt us hardened, as we are still trying to perform, and bring others into the unattainable bondage to KEEP to law. This is the nature of those who hold the letter in the esteem that only the Spirit deserves. Jesus is Lord, as the Spirit IS the Spirit of Christ Himself, you see.
I would suggest a strategy with this person. Do not respond to their Scripture spouts with your ideas about scripture; this is what they feed on. Begin to respond to their strifes with a testimony glorifying Christ by the Spirit; IE, How Jesus moved in situations and lives BY HIS SPIRIT.
This is indisputable TESTIMONY that thrusts the dialogue upon the right ground; your own personal book of acts...and acts of your Holy Spirit. This may unnerve your friend, but remain there, in love, and perhaps they may see their depravity and uselessness to exalt scripture alone as justification and a covering for their faith.
We overcome one way, and scripture is important, but.... "And they overcame him by the blood of the Lamb and by the word of their testimony, and they did not love their lives to the death. "
Our faith must lie in a living God on high, not in the written word that He left us , alone.
The letter kills, but the spirit gives life.