Okay, so back to your example. If someone says they are saved, knows the Lord commands water baptism, and yet refuses to obey, are they truly saved?
So you think failing to be water baptised is the same as murder?
Overall, there are two groups of people. Saved saints and unsaved sinners. As believers, we treat these two groups differently.
The saved: if they sin, there is a scriptural method of handling this. Essentially, to go to them. And ultimately, to throw them out of the church and treat them as sinners.
1 Cor 5:11 But actually, I wrote to you not to associate with any so-called brother if he is an immoral person, or covetous, or an idolater, or a reviler, or a drunkard, or a swindler—not even to eat with such a one.
So, does refusing water baptism fall into this list, immoral, covetous, idolator, reviler, drunkard or swindler? That is our list.
Or another list, but this list is the fruit of the Spirit, meaning it is the fruit produced by the Holy Spirit in a believers life. We bear, or hold up the fruit, but we don't produce the fruit. In my view, the fruit of the Spirit is something which develops over time for anyone who has the indwelling Holy Spirit, because the Spirit will produce this fruit. The fruit of the Holy Spirit is actually a sign of maturity.
Gal 5:22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness, self-control; against such things there is no law.
For the unsaved, we are not to judge them, for God will be their judge. We are to share the gospel with them and treat them well, although not as brothers in the Lord.
What are the deeds of the flesh?
Gal 5:19 Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality, 20 idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, 21 envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God.
Does this mean a new believer, who has outbursts of anger (anger issues), is actually not saved? No. We are talking about a new believer or a carnal Christian. Being conformed to Messiah is a process. But, as a new believer, refusing water baptism is not in the list of the deeds of the flesh either.
1 Cor 3:1 And I, brethren, could not speak to you as to spiritual
people but as to carnal, as to babes in Christ. 2 I fed you with milk and not with solid food; for until now you were not able
to receive it, and even now you are still not able; 3 for you are still carnal. For where
there are envy, strife, and divisions among you, are you not carnal and behaving like
mere men?
And there is the point. A new Christian, although filled with the Spirit, is likely carnal, and in need of the steady teaching of the Holy Spirit, to conform them to Messiah.