From First and Second Peter, Jude (Coming November 2011) by Daniel Keating, commenting on 1 Peter 1:6-7:
Peter introduces a profound paradox: the presence of inexpressible joy in the midst of suffering. He says first that we rejoice in this living hope, which is our salvation, present and future. Who would not rejoice? But then he tells us that now we must be ready to suffer through various trials, even if only for a little while.
Using a metaphor found frequently in the Old Testament (Job 23:10; Prov 17:3; Wis 3:5-7; Zech 13:9), Peter compares the testing of our faith to the purification of gold by fire. The sentence structure is difficult to follow, but the point of the comparison is perfectly clear. If gold, the most precious of earthly substances, requires purification, how much more does our faith—more precious than any earthly gold—benefit from the purifying fire of our trials. “For in fire is gold tested, and worthy men in the crucible of humiliation” (Sir 2:5).