Found just once in the New Testament (Heb. 6:6Heb. 6:6
English: American Standard Version (1901) - ASV
6 and then fell away, it is impossible to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.

WP-Bible plugin), the Greek verb “anakainizo” meant “renew” or “restore.”  Those who “fall away” (forsake the Christian faith) cannot be “renewed” (restored) to “repentance.”

If people try to go back and serve God under the Old Testament system of religion, they cannot find an acceptable sacrifice for sin.  In fact, those who turn to the Old Testament system of religion (and by implication any other system besides Christianity) “crucify the Son of God afresh” (Heb. 6:6Heb. 6:6
English: American Standard Version (1901) - ASV
6 and then fell away, it is impossible to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.

WP-Bible pluginb).