Thomas Boston, Works, 3:235-236:
It will always be well with those who take part with truth and holiness, setting themselves against the flood of sin in an ungodly and unrighteous generation. “Say ye to the righteous, that it shall be well with him; for they shall eat the fruit of their doings.”
If you do prevail in any measure to stop the flood of sin, so far as you do prevail, you bring honour to God, who is dishonoured by ungodly and unrighteous practices. “Let your light so shine before men, that they may see your good works and glorify your Father which is in heaven.” You also bring safety to perishing souls, and oh! what should not one do to save a soul from death. “Let him know that he which converteth the sinner from the error of his way, shall save a soul from death, and shall hide a multitude of sins.” You also strengthen the cause of religion by making friends to it, and weaken Satan’s kingdom.
But though you should not prevail, yet you give your testimony for God. “They that forsake the law praise the wicked; but such as keep the law contend with them.” And you deliver your own souls from the guilt of the common conspiracy. You take the best way for safety in the evil day. “And the Lord said to him, go through the midst of the city, through the midst of Jerusalem, and set a mark upon the forehead of the men that sigh and that cry for all the abominations that be done in the midst thereof.” So that you shall either be delivered from trouble or in trouble.
Source: http://www.puritanboard.com/f25/setting-themselves-against-flood-sin-83751/, Comment #1 (Thank You, Reverend Winzer!)