From Andrew Fuller's Journal
Question:- Was David not a regenerate man when he slew Uriah by the sword of the children of Ammon; and if so, how can we reconcile his conduct with the apostle's assertion, that "no murderer hath eternal life abiding in him?" (1st John 3 verse 15 "Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him.")
Answer:- the difficulty here suggested would vanish, if it were considered that, while the quality of actions is determined by their relationship to God's law, the estimate we form of a person's character must be regulated by the habitual course of the life and conduct in question. Thus, if we were to form our opinions of men from particular events in their lives, we should pronounce Noah a drunkard, Aaron and idolater, Jacob a liar, David a murderer, and Peter an apostate - and each of these characters is excluded from the kingdom of God. But such a judgment would evidently be harsh and erroneous, because these things were not of a piece with their general character, but most entirely opposed thereto. The apostle, in the words referred to, is describing those who "go in the way of Cain," and whose character and spirit resemble his. Such a man, he affirms, "hath not eternal life abiding in him."
But in this sense David was not a murderer. His sin, in the matter of Uriah, was not the result of those principles on which his character was formed, but a melancholy proof of the force of temptation even in the case of an eminently good man.