John Gill Commentary 1 Chronicles 28:20

"And David said to Solomon his son, Be strong and of good courage, and do it: fear not, nor be dismayed; for Jehovah God, even my God, is with thee; he will not fail thee, nor forsake thee, until all the work for the service of the house of Jehovah be finished." — 1 Chronicles 28:20 (ASV)

And David said to Solomon his son, be strong, and of good courage, and do it (See Gill on 1 Chronicles 28:10)

fear not, nor be dismayed; that you shall meet with any opposition in the work, or not be able to finish it for want of materials and workmen, or money to pay them:

for the Lord God, [even] my God, will be with you; to guide and direct, prosper and succeed; the Targum is, "the Word of the Lord God, my God, will be your help:"

he will not fail you, nor forsake you; a promise made to Joshua, and is applicable to every good man in whatsoever good work he is concerned, (Joshua 1:5) (Hebrews 13:5)

until you have finished all the work for the service of the house of the Lord; built the temple, and all the apartments of it, and courts belonging to it, and made and provided all the utensils and vessels necessary for the service and worship of God.