***Because, as you say, it is mentioned only in the Epistles.***
I DIDN’T say it was ONLY in the epistles. You said it wasn’t even in the Bible. I showed you one place where it is. Others:
Direct my footsteps according to your word; let no sin rule over me.
How can a young man keep his way pure? By living according to your word.
Your statutes are my delight; they are my councilors.
My soul is weary with sorrow; strengthen me according to your word.
Turn my eyes away from worthless things; preserve my life according to your word.
And much much more. Sanctification is rampant throughout the Bible. All these came from one psalm.
***The term does not appear in the Bible save for the Epistles, so no other Apostle, who actually knew Christ in Person, taught it or knew it for that matter.***
Then why does 1 Peter (who was not Paul) mention sanctification in verse 2 of chapter 1?
Keep jumping.
I was making a comment about what FK posted, namely: "Once a low level true faith is established by God (salvation), then sanctification begins and we move toward a higher level. This movement not only benefits us personally in our personal relationship with God, but it also makes us more useful to God to accomplish His plan for us as individuals. A fully saved person can and will always grow in Christ."
You extracted one word out of it, instead of the whole context. Where is the mention of God's plan in the Bible? Stop obfuscating the issues by taking things out of context.
Then why does 1 Peter (who was not Paul) mention sanctification in verse 2 of chapter 1?
1 Peter was written in Pauline style to pacify the rift between him and Peter. 1 Peter is distinctly Pauline in character and language.