惟有

Only such a striver is valuable.

惟有这样的奋斗者才是有值的。

The ancient people who was successful, not only had exceptional talent but also had unflinching will.

古人立大事者，不惟有超世之才，亦必有望忍不拔之志。

But inapt as I am, will follow your advice and perform my duties to the best of my powers.

虽不才如，当谨如尊谕，力所能及者惟有勉尽天职也。