An excerpt from Affectionate Guidance:
Devotee: In Srimad Bhagavad Gita, Krishna has explained about karmma-yoga. Can karmma-yoga ever be seva, or devotional service?
Srila Govinda Maharaj: Karmma and seva, action and divine service, are identical from the external perspective. Bhakti-yoga and karmma-yoga are the same apart from one thing—and that is the inner mood of the practitioner. The inner intention is the all-important, differentiating factor.