From Bruce R. McConkie, "Be Valiant in the Fight of Faith," Ensign, Nov. 1974, pp. 33-35.
In this war all who do not stand forth courageously and valiantly are by that fact alone aiding the cause of the enemy. "They who are not for me are against me, saith our God." (2 Ne. 10:16)
Members of the Church who have testimonies and who live clean and upright lives, but who are not courageous and valiant, do not gain the celestial kingdom. Theirs is a terrestrial inheritance. Of them the revelation says, "These are they who are not valiant in the testimony of Jesus; wherefore, they obtain not the crown over the kingdom of our God." (D&C 76:79)
Now what does it mean to be valiant in the testimony of Jesus:
It is to be courageous and bold; to use all our strength, energy, and ability in the warfare with the world: to fight the good fight of faith. . . . The great cornerstone of valiance int eh cause of righteousness is obedience to the whole law of the whole gospel.
To be valiant in the testimony of Jesus is to come unto Christ, and be perfected in him; it is to deny ourselves 'of all ungodliness.' and 'love God' with all our 'might, mind and strength.' (Moro. 10:32)
To be valiant in the testimony of Jesus is to believe in Christ and his gospel with unshakable conviction. It is to know of the verity and divinity of the Lord's work on earth.
But this is not all. It is more than believing and knowing. We must be doers of the word and not hearers only...
To be valiant in the testimony of Jesus is to 'press forward with a steadfastness in Christ, having a perfect brightness of hope, and a love of God and of all men.' IT is to 'endure to the end.' (2 Nephi 31:20.) It is to live our religion, to practice what we preach, to keep the commandments. It is the manifestation of 'pure religion' in the lives of men; it is visiting “the fatherless and widows in their affliction” and keeping ourselves “unspotted from the world.”