As studies of second language (L2) learning and motivation typically focus on English as a foreign language (EFL), L2 motivation for Arabic has been less studied. Instruments measuring two sources of L2 Arabic motivation, identity-related motivation, and motivation arising from the L2 learning environment (L2LE), were developed and piloted among L2 Arabic learners. Pilot study results showed strong motivation due to Islamic identity and desire for cultural exposure, but also revealed speaking anxiety in the L2LE. In this study, the objectives were to determine: a) What evidence exists for or against the validity of the subscale measurements from these instruments? and b) how this evidence can be used to explain what appear to be contradictions in the pilot study results. In this mixed-methods study, instruments were administered twice to learners at an L2 Arabic learning institute in the Kingdom of Saudi Arabia (KSA), and a sample was interviewed. Quantitative analysis showed evidence of instrument reliability, and analysis of interview data revealed several findings. First, consistent with pilot data, we found that learners, who were all Muslim, were motivated to learn L2 Arabic as part of desiring cultural and social exposure in KSA and to become closer to Islam. Interview data revealed that these learners aimed to adopt the customs and lifestyle of those in KSA as part of becoming closer to Islam, some of which they did through social interaction. Second, L2 Arabic learning of Classical Arabic (CA) at the institute was impeded by the learners’ lack of knowledge of the conversational Modern Standard Arabic (MSA) dialect, which made practical communication with those in KSA difficult. Recommendations are made for instrument improvement, as well as a strategy to incorporate some MSA instruction into the CA curriculum.