Leviticus 21:14
A widow, or a divorced woman, or profane, or an harlot, these shall he not take: but he shall take a virgin of his own people to wife. A widow, or a divorced woman, or profane, or an harlot, these shall he not take: but he shall take a virgin of his own people to wife.
The instruction stands as part of the directions in Leviticus 21:6-23 that required all who ministered in the sanctuary to be pure and holy and without blemish. Such strictness was demanded because their work brought them into close connection with God. The prohibition against taking a widow or a divorced or profane woman or a harlot, and the requirement to take instead a virgin of his own people to wife, belongs to that same requirement of holiness for the ministry. God remains just as holy now, and just as particular that those connected with His work meet that standard.