Christ expounds the Day of Atonement / Judgment Day, and there's a curious note in this verse. Though the verse describes its own content as being a "parallel," there's an odd element out. If people are good, they go to everlasting life, according to Christ's mercy; if they are bad, they go to damnation, according to Christ's justice.
So what is the role of Christ's "holiness" in the verse?
Holiness is power, efficacy, the ability to get things done. Without his holiness, Christ's justice and mercy would not accomplish the great works they do.