This verse describes a specific detail in the creation of the priestly garments for Aaron and his sons, as detailed in the book of Exodus. Let's break down what it means:

"They tied to it a lace of blue...": This refers to a specific part of the high priest's attire, specifically the tzitz or holy crown/plate. The "lace of blue" is a cord made of blue thread (Hebrew: tekhelet) used to attach this plate to the turban. Blue was a very important color in the tabernacle and priestly vestments, often associated with divinity and heaven.

"...to fasten it on the turban above...": The turban (Hebrew: mitznefet) was the head covering worn by the priests. The blue cord was used to secure the golden plate onto the front of the turban. This plate was a prominent symbol of the high priest's office.

"...as Yahweh commanded Moses.": This is the crucial point. This entire process, including the materials used (like the blue thread) and how they were assembled, was done according to the precise instructions given by God (Yahweh) to Moses. This underscores the importance of following God's explicit directions in matters of worship and ritual. It emphasizes that the priests' garments were not simply clothing, but sacred vestments designed according to divine specifications, with symbolic meaning. The holy crown had the inscription "Holy to the Lord" engraved upon it.

In Summary:

The verse describes a seemingly small detail in the fashioning of the high priest's garments: the blue cord used to secure the golden plate to his turban. However, its significance lies in the fact that this detail, like all other aspects of the tabernacle and its service, was meticulously carried out "as Yahweh commanded Moses." This highlights the importance of obedience, divine authority, and the symbolic nature of the priestly garments as divinely ordained.

The "lace of blue" is a constant reminder that the high priest's role and authority came from God.