"Deep seriousness" refers to a state or quality of being very serious or sincere about something. It implies a level of earnestness and importance attached to one's thoughts, actions, or attitudes. Full definition
With a passion touched by poignancy, Elshtain offers this concluding reflection: «The task of the democratic political imagination is possible if civility is not utterly destroyed, if room remains for playful experimentation from deep seriousness of purpose free from totalistic intrusion and ideological control. (firstthings.com)
But if they are taken in connection with the sayings of Jesus — irrespective of whether they were really spoken by him or were brought into this context by the church — they do not acquire a different meaning, but they are counterbalanced by other sayings in which the reality of man's life is discerned with a deeper seriousness. (religion-online.org)
This spirit of romp exists in tension with a deeper seriousness, just as an odd solemnity is noticeable when children are at play. (religion-online.org)