Paul's reflection on 'speaking in tongues' has been widely discussed and debated both in the public and academic domain. Adequate attention has not been given to the explicit citation presented in 1 Corinthians 14:21 (Isa. 28:11-13a) in general, and the term έτερόγλωσσος together with the phrase λέγει κύριος in particular in addressing the issue of γλώσσα. The aim of this article is to revisit the issue of γλώσσα in 1 Corinthians 14 through the lens of 1 Corinthians 14:21. This will entail meticulous analyses of έτερόγλωσσος together with the phrase λέγει κύριος. The ultimate objective is to come to a better understanding of Paul's reflection, hence his conception of γλώσσα, from the perspective of 1 Corinthians 14:21. To achieve these objectives it would be necessary to first discuss the concept underlying 1 Corinthians 14:21 in terms of the immediate literary context. Second, the literary context of this source text should be determined, evaluated and discussed. Third, the impact of έτερόγλωσσος and λέγει κύριος in terms of γλώσσα should be determined and explained. Finally, some conclusions will be drawn regarding Paul's reflection on γλώσσα.