The phrase "was earnest" can be replaced with a variety of synonyms that convey the same level of sincerity and seriousness. Some options include "was genuine," "was sincere," "was committed," "was dedicated," "was zealous," "was impassioned," "was wholehearted," "was resolute," "was determined," and "was honest." Each of these words captures a different aspect of the quality of earnestness, from a sense of authenticity and honesty to a powerful drive to achieve one's goals. By using these synonyms, you can add nuance and depth to your writing or speech and communicate your message with clarity and precision.