We all wear disguises on occasion. Sometimes we do it because we have to, sometimes just because it's become a habit. Then there are times we use disguises to keep us feeling safe, maybe even predictable. However we use them, the fact still remains that we're hiding something. If we're dishonest about our disguises (pretending to be someone we're not), then we're certainly not doing ourselves any favors, according to our speaker. More than that, we're being distracted because we're too busy covering up the reality of life, rather than striving to embrace it in the moment.
Lines 4-5: The "wenches" are instructed to "dawdle in such dress as they are used to wear." They're not being told to doll themselves up in evening gowns and fur coats or funeral attire, for that matter. Rather, they should wear what they're used to wearing, which will more honestly reflect who they are.
Line 7: This is one of the more powerful lines that's getting at the reality behind the disguise. "Seeming" is the disguise while "be" is the reality. Here, the speaker is calling for the "finale" of "seeming," which would ideally be the pure reality—not the disguise.
Lines 10-14: Here we get the dead woman's sheet of "fantails" that is used to "cover her face." Fantails are highly decorative so they do a good job of covering up things. The fact that the sheet covers her face tells us that, even in death, appearances are important to us. The face is hidden so that we can put some small barrier between us and the reality of death. Notice, though, that—for all her fantail embroidering, and this attention to appearance—her feet still stick out. Dead, at the end of the day, is dead—regardless of anyone's attention to appearances.