D&C 60

As many of the Elders were about to return from Zion to Kirtland, the Lord said to them -

"...with some I am not well pleased, for they will not open their mouths, but they hide the talent which I have given unto them, because of the fear of man. Wo unto such, for mine anger is kindled against them." (Doctrine and Covenants Section 60:2)

The Lord has made it clear -

"...it becometh every man who hath been warned to warn his neighbor." (Doctrine and Covenants Section 88:81)

And we are to do it by opening our mouths. The wicked priests of King Noah's court asked Abinadi -

"...What meaneth the words which are written, and which have been taught by our fathers, saying:
21 How beautiful upon the mountains are the feet of him that bringeth good tidings; that publisheth peace; that bringeth good tidings of good; that publisheth salvation; that saith unto Zion, Thy God reigneth..." (Book of Mormon Mosiah 12:20 - 21)

After teaching them the doctrine of Christ, Abinadi answers -

"...every one that has opened his mouth to prophesy..." (Book of Mormon Mosiah 15:13)

...or to bear testimony -

"...these are they who have published peace, who have brought good tidings of good, who have published salvation; and said unto Zion: Thy God reigneth!" (Book of Mormon Mosiah 15:14)

Opening our mouths at times is a difficult thing. We don't necessarily want to offend anyone. Joseph Fielding Smith wrote of these early Elders in the Church -

"They had been commanded to preach the Gospel along the way and bear testimony among the people, but some had failed to magnify this commandment because of their fear of man. It is true that not every man is a natural missionary, and there are those who shrink from the responsibility of raising their voices in proclamation of the Gospel, and yet this is an obligation that we owe to this fallen world. The elders in the very beginning had been commanded to serve the Lord with all their ‘heart, might, mind and strength,’ for the field is white and ready for the harvest. A penalty was to be inflicted upon those who failed and they were not to stand blameless at the last day. The preaching of the Gospel was to be a means to them by which they were not to perish, but bring salvation to their souls. There are many who have been sent forth who have had a fear of man, yet the Lord has promised to support them in their labors if they will trust in him." (Church History and Modern Revelation, 1:220–21.)