“The Steadiness of Thy Brother”

Joseph F. McConkie, Robert L. Millet
This seems to be a specific reference to Shiblon, although Helaman was also a noble example.

“They Were Filled with the Holy Ghost”

That is, they enjoyed the gifts and powers of the Spirit in their ministry: discernment, prophecy, revelation, knowledge wisdom, the ministry of angel, charity and many others. Having been sanctified from sin, they had their hearts and mouths filled with holiness and with heavenly power. They spoke what was given them from above. Their words enjoyed the justifying and sustaining power of God.

Doctrinal Commentary on the Book of Mormon, Vol. 3

References