What do lines 5-6 of the "Morning Song" (by Sylvia Plath) mean by saying "your nakedness shadows our safety?"

Sylvia Plath's "Morning Song" portrays a scene of childbirth and offers the mother's perspective on her newborn child. The poem begins with the child's birth in the first two stanzas. Plath writes,

Love set you going like a fat gold watch.
The midwife slapped your footsoles, and your bald cry
Took its place among the elements.
Our voices echo, magnifying your arrival. New statue.
In a drafty museum, your nakedness
Shadows our safety. We stand round blankly as walls. (1-6)

The baby enters the world, his/her time on earth beginning "like a fat gold watch." The baby is slapped into awareness by the midwife, and the baby's cry becomes part of the world his parents inhabit.
The second stanza contains the lines you are to analyze. In this stanza, the parents' reaction to the child's birth is conveyed using imagery and word choice related to a museum. This museum is "drafty" and silent. In this space, the parents' "voices echo," which only serves to further highlight the child's arrival. The baby is figuratively compared to a "New statue." Like a nude statue in a museum, the baby's "nakedness / Shadows our safety." This alliterative line is quite ambiguous. The word "safety" evokes a warm feeling, but "Shadows" is definitely more ominous. The parents' world seems darkened in some way by the arrival of the child. This could be because the parents now realize in a more direct way the responsibility of rearing the child. It could also be a result of the baby's birth making the adults reflect on their own mortality.
The speaker's ambivalence toward motherhood continues throughout the remainder of the poem. She is devoted to her child, waking at its cry and trying to soothe it. However, the imagery Plath uses in these stanzas suggest the mother feels distant from her child. She says that "A far sea moves in [her] ear" and that the child's sounds "rise like balloons" (12, 18). The distance of the sea that metaphorically sounds in the speaker's ear and the distance and departure conveyed by the simile of the balloons drifting away from the speaker, both suggest the speaker's ambivalence. Like the earlier image of the statue, these figurative comparisons tell the reader that the close bond we assume between mothers and children cannot always be simply assumed.