1 Corinthians 3:12

Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble (KJV)

Then: Gold, silver and precious stones were construction materials used in building the temple. Paul is preparing the Corinthians for his upcoming thoughts in vs 16. Obviously, he's referring to spiritual foundations, not actually physical ones. He teaches through a the third metaphor in a series of four: laborers, fields, foundations, temples. Is the building of great value made from beautiful materials or poorly constructed with perishable materials? Will it stand in the final judgement? Wesley broadens the thought from solely personal applications to a concern for the church as a whole. He states any doctrines, ceremonies, or other man-created additions to the worship of Christ cannot stand the fire. Wright (p. 37) expands his discussion to the conflict between builders and destroyers. Paul's concentration on the Corinthian problem of divisions became a straight line-wind coming down on the Corinthians; not to destroy, but to purify before the last days.

Now: These words and what follows make all readers cringe as they question their personal work. "What is the quality of my work? Is it long-lasting and solid like gold, silver, or other stones which can withstand fire, or is it not?" The question deals with one part of a Christian, the temple. The other part of the person - the servant - emerges as the temple is built.

Extra source: John Wesley's Notes on the New Testament by John Wesley (on-line version: publisher and date not listed) http://www.ccel.org/ccel/wesley/notes.i.viii.iv.html