Read Exodus 28:28 Using Other Translations
And they shall bind the breastplate by the rings thereof unto the rings of the ephod with a lace of blue, that it may be above the curious girdle of the ephod, and that the breastplate be not loosed from the ephod.
And they shall bind the breastpiece by its rings to the rings of the ephod with a lace of blue, so that it may lie on the skillfully woven band of the ephod, so that the breastpiece shall not come loose from the ephod.
Then attach the bottom rings of the chestpiece to the rings on the ephod with blue cords. This will hold the chestpiece securely to the ephod above the decorative sash.