John Gill Commentary Isaiah 41:7

"So the carpenter encourageth the goldsmith, [and] he that smootheth with the hammer him that smiteth the anvil, saying of the soldering, It is good; and he fasteneth it with nails, that is should not be moved." — Isaiah 41:7 (ASV)

So the carpenter encouraged the goldsmith The carpenter, when he had made a wooden image, encouraged and hastened the goldsmith, or the "finer", as some render it, to do his part, in covering it with plates of gold or silver.

and he that smoothes with the hammer him that smote the anvil He that beat out thin plates of gold and silver with the hammer, in order to decorate the wooden god, encouraged the smith at the forge, that smote on the anvil, there making nails for the fastening it to a pillar or wall, to hasten his work.

saying, it is ready for the soldering For the several joints to be put together, by soldering them.

and he fastened it with nails, that it should not be moved Either the goldsmith and finer fastened the plates of gold and silver with nails, that they might be kept fast and close to it; or the smith that smote on the anvil, and made the nails, he fastened the image with them at some proper place, that so it might not fall, or be taken away. All which, as it represents the hurry and solicitude idolaters were in to keep up their craft and religion, so it exposes them to ridicule and contempt.