The missing word in this sentence is "stronger". Therefore, the complete sentence is:
"The Student t critical value is larger (farther to the right), showing that with the Student t distribution, the sample evidence must be stronger before we can consider it to be significant."
This means that for a given level of significance, we require more evidence (a larger t-value) to reject the null hypothesis when we are using the t-distribution, as compared to when we are using the standard normal distribution.