The term originated in ancient Israel. The farmers would plow their fields by using oxen. If the ox didn't want to follow the guidance of the farmer it would stiffen the muscles in its neck. This would make it impossible to guide the ox where it needed to go.
When one is described as "stiff-necked" in the scriptures it means that they refuse to follow the guidance of the Lord.
You're a bunch of hard heads, stubborn.
Stubborn.
Deuteronomy 6:5
The word sanctify is not found in this verse. The verse speaks of having a chosen people who are special and set apart from others
Refer to Deuteronomy 6.
These are the words mentioned in verse 6. In verse 7, teach them to your children. In verse 8, have them on your hand as a sign. In verse 9, write them on the posts and gates of your house. For a fuller description of the narrative in Deuteronomy, with commentary, please visit: http://christianity.answers.com/bible/the-book-of-deuteronomy
Hear, O Israel! The Lord your God, is one!
The passage sets out the monotheistic nature of Israel's faith and the importance and blessings of obedience to God's commandments especially the command to love Him.
Deuteronomy chapter 6, verse 4
Different individuals may consider different verses as the most important to them based on their beliefs and interpretations. However, one verse that is often cited as significant is John 3:16, which highlights the message of God's love and sacrifice for humanity through Jesus Christ.
The ten commandments appear first in Shmot (Exodus) in chapter 20, verse 1 and continue through verse 14. They appear again in (Devarim) Deuteronomy chapter 5, verse 6 and continue 18.
Deuteronomy 6:5
It's not exactly the same as what you're asking, but see Deuteronomy 23:6.
One verse that supports the idea of eternal salvation is John 10:28, where Jesus says, "I give them eternal life, and they shall never perish; no one will snatch them out of my hand." This verse emphasizes the security of those who believe in Jesus and highlights the permanence of their salvation.