Is the use of instrumental music in worship a salvation issue? For example, regarding the division between instrumental and non-instrumental churches of Christ, if in the end when Christ returns both churches are still divided and convinced of their own views on the issue, will all of them that otherwise have remained faithful to God be saved?
Your real question is how important is obedience to being saved. The use of the phrase "salvation issue" is simply the way some men try to rate God's commands as to their importance. If a command isn't seen as directly affecting a person's salvation, then it is assumed that it can be safely ignored.
But consider these:
- Was the source of fire for the altar of incense a salvation issue? God didn't even directly state that only one source had to be used, and yet Nadab and Abihu found out it did matter to God (Leviticus 10:1-2). They lost their lives over this seemingly minor issue.
- Did matter that Moses struck the rock while speaking to the people? God told Moses to speak and He told him to take Aaron's rod; He just didn't mention whether the rod was to be used or not. Yet Moses could not enter the Promise Land because of this one small incident (Numbers 20:7-12).
- What about when Saul kept back some of the animals and one man when he was ordered to destroy a nation? Was that a salvation issue? Yet Saul lost his kingdom because of it (I Samuel 15:1-23).
- Surely keeping the ark from falling over wasn't a salvation issue. But Uzzah lost his life because of it (II Samuel 6:1-7).
- And that small lie concerning the amount of money given to the church, that couldn't have been a salvation issue, could it? But once again we find Ananias and Sapphira losing their lives over this seemingly small incident (Acts 5:1-11).
The very claim of faith demands that we obey God. Israel could not enter the promised land because of their disobedience. "And to whom did He swear that they would not enter His rest, but to those who did not obey? So we see that they could not enter in because of unbelief" (Hebrews 3:18-19). It is faith that spurs us to obey God. "Now to Him who is able to establish you according to my gospel and the preaching of Jesus Christ, according to the revelation of the mystery kept secret since the world began but now has been made manifest, and by the prophetic Scriptures has been made known to all nations, according to the commandment of the everlasting God, for obedience to the faith -- to God, alone wise, be glory through Jesus Christ forever. Amen" (Romans 16:25-27).
When we claim to love God, that love implies we will be obedient. "If you love Me, keep My commandments" (John 14:15). "For this is the love of God, that we keep His commandments. And His commandments are not burdensome" (I John 5:3).
In other words, disobedience demonstrates that we do not believe God really meant what He said and that we don't really love Him. Obedience is critical to our salvation; thus, every command of God is a "salvation issue."
"Therefore, my beloved, as you have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling; for it is God who works in you both to will and to do for His good pleasure" (Philippians 2:12-13).
"Let us therefore be diligent to enter that rest, lest anyone fall according to the same example of disobedience" (Hebrews 4:11).