Like it or not, life is change. You are no longer the same person you were one minute ago. By default, we are changed by time and by the world. We are also changed by the choices we make (which is why Shmoop is feeling remorseful about that second hot fudge sundae). "The Wild Iris" lends itself to many interpretations, but the poem seems particularly interested in two types of transformation: emotional and spiritual. Both involve suffering, but both arguably lead to freedom.
"The Wild Iris" suggests that suffering can lead to emotional growth because painful experiences sometimes strengthen a person's character by breaking old habits and revealing new possibilities.
"The Wild Iris" suggests death is not an end. It's just yet another change we undergo.