1 Jude, a bondservant of Jesus Christ, and brother of James, To those who are called, sanctified by God the Father, and preserved in Jesus Christ: 2 Mercy, peace, and love be multiplied to you.
téreó v def to keep, to guard, to watch over
Téreó here in Jude 1 and in 1 Thessalonians 5:23 is translated preserved. The aorist tense of the verb indicates that the continuous preservation of the believer is a single, complete act, regardless of when it is accomplished.
The preservation (keeping) occurs in Jesus Christ. This is important since the strength of the keeper determines the permanence of the kept. In these two places in Scripture, as well in others, we see that the believer is not in control of the permanent state of justification.
Sanctified is synonymous with holiness. See Holy.