The Menorah that was constructed for the Tabernacle had to be made out of a single hammered piece of pure gold (Exodus 25:36).
This is expressed in Hebrew as “kula miksha achat zahav tahor”. The word ‘miksha’ also carries the connotation of hard or difficult.
The most difficult thing to find is pure gold! Too often, money issues bring out the worst in people. The Midrash teaches that when contributions came in for the Tabernacle, Betzalel was able to sense the purity of intention behind each gift. The purest contributions were used for the most important and holiest parts of the Tabernacle.