If I may add to what dear tec and wasblind said (may you all have peace, and thank you!), this issue was about three (3) things:
1. Abraham's faith... IN GOD'S PROMISE:
"... it is by means of Isaac that what will be called your seed will be..."
The question here was whether or not Abraham truly BELIEVED that promise, had FAITH in it (i.e., "the ASSURED EXPECTATION of the thing hoped for, the EVIDENT demonstration of reality... though NOT beheld"). The Most Holy One of Israel had PROMISED Abraham that by means of THIS son, Isaac (by, Sarah, the wife Abraham LOVED)... Abraham would have more seed. As the sands of the sea. Abraham had every right to HOPE for fulfillment of that promise, therefore... and thus, have an assured expectation of it. Why? Because... Sarah CONCEIVED Isaac (at age 90!)... based on a PROMISE from God... which promise was FULFILLED. Isaac's conception and birth was the "evident demonstration"... of the reality that such seed WOULD come into existence... THROUGH him... even though that seed had not come into existence ("though not beheld")... although God was now seemingly asking something that would make it virtually impossible!
2. My Father, the Most Holy One of Israel knew that Abraham loved Him. The question was... how MUCH? God tested Abraham's faith in this way in order to find that out. He had to be CERTAIN that Abraham was the man He (God) knew he (Abraham) was: one whose love for his own flesh (Isaac) was NOT greater than his love for the Most Holy One of Israel:
"... he that has greater affection for son...than for me is not worthy of me." (Certainly, if this applies to the Holy One of Israel, JAHESHUA MISCHAJAH, how much MORE would it apply to the MOST Holy One of Israel, his God and Father, JAH of Armies!)
WHY did this "affection" need to be tested? Why did it matter? Because:
3. My Father, the Most Holy One of Israel, JAH of Armies, was going to sacrifice HIS Son, thus HIS "seed"... my Lord, JAHESHUA MISCHAJAH... for Abraham. First and foremost. And for Abraham's seed, second... because of His love for Abraham (which is WHY there are 144,000 "from among the sons of Israel"). And, third... for the world: those NOT of Abraham... or Isaac... or Jacob... or Judah... but who put FAITH... in the PROMISE made to Abraham, Isaac, Jacob, Judah... and David. Because of HIS love... for the world (John 3:16, 17).
For this, all it took was for ONE man from among earthling man to demonstrate... HIS faith in God's promise regarding that sacrifice (i.e., the "seed" that was to BE that sacrifice). Abraham... was that man. Not only was he to believe in that seed (Christ)... but that seed was PROMISED to come through Isaac. Abraham not only had to "exercise" faith in that promise, that it would come through Isaac... but it would be fulfilled EVEN if Isaac were sacrificed first. He had to "demonstrate" HIS "assured expectation"... in this, the "thing hoped for": a reconcilation to God... and return to the status lost by Adham, by means of the Seed, Christ.
But what of today? What of those who "hear" a "voice" telling them to kill their child... for whatever reason? Or kill anyone for ANY reason (other than self-defense/defense of others)? The ONLY "sacrifice" that the Most Holy One of Israel sanctioned... EVER... was that of HIS OWN SON. No other. Not even Isaac. The Most Holy One of Israel does not tell us to kill our children... for ANY reason. He doesn't even tell us to SHUN our children... for ANY reason. How do we know? Because TODAY... He speaks to us by means of HIS Son... and that Son (1) NEVER said, taught, or required any such thing... as can be found in what is recorded of him (and he is recorded to have said that everything HE did, he learned from the Father and he did what he saw the Father doing)... and (2) NOR does he when he speaks to one directly! He cannot. Why? Because... he is the LIFE (John 14:6)... and the source of life. NOT Death... or the source of death. THAT, dear ones, is our Adversary, the one called "Satan" and "Devil."
What, then, "... should a [christian] do if he suddenly hear [the voice of God] telling him to slit the throat of a family member?"
If s/he truly is a christian s/he would simply OPPOSE it and, in the name of God/Christ, tell its source to go away, move on, get lost, take a hike/powder... and leave her/him be. And... it would. Because it is the christian that has authority over such a source, not the other way around! Certainly, if those who do NOT know Christ (who are not known BY Christ) can cast out demons, those who ARE known by Christ can!
But why would s/he "simply" do this? Because s/he would KNOW that:
1. It is NOT the voice of God, because although the Most Holy One of Israel USED to speak to Israel through His Prophets, He NOW speaks... through His Son... who is His Word and Holy Spirit. (John 1:14; Hebrews 1:1, 2; 2 Corinthians 3:17; Revelation 19:13). If s/he were unsure (because, among other things, Satan "keeps transforming himself into an angel of light"), s/he would question the voice and demand that it reveal itself as to its true identity (Mark 5:9; Acts 9:5)...
2. That Son communicates with us (christians) by means of holy spirit ("living water"), which spirit would NEVER direct us to do an unrighteous act (John 4:14, 7:38; John 20:22;1 John 2:26, 27), and...
3. The Most Holy One of Israel IS "Love"... and that His Son IS "the [Tree of] Life"... and that God GAVE that SON... as the FULL AND COMPLETE "sacrifice"... once and for all time... so to even make such a directive would be IMPOSSIBLE... because it would have absolutely NO "value" or benefit (and if the argument is "Yeah, what about the things Paul taught?" the response is, yes, well, nothing like that was EVER requested by Christ, who is the "exact representation" of God's very being... which Paul wasn't, isn't, and never will be).
If he were a christian, he would know these things by means of the anointing... that resulted in him being a "christian." (John 4:14, 7:38; John 20:22;Acts 2:2-4, 10:47;1 John 2:26, 27).
Forgive me, dear Bohm, but your question incited the spirit in me... because it asks what a "christian" should do. Just like not all who profess to be Israel ARE Israel (Revelation 3:9), not all who go by the designation "christian" ARE truly christians. A "christian" is not something one "becomes" because one joins a church or religion. Or because one professes to follow the teachings of Christ - that is a "disciple." Many of Christ's disciples left off following him (John 6:66); rather, a christian is a "chosen/anointed" (christ) "person" (ian)... such choosing/anointing done by an "anointing" with the "oil [of exultation]"... which "oil" is holy spirit: God's life force, which is manifest in His breath, blood, and semen... and referred to by Christ as "living water." That is why is it referred to as being "poured out" upon those who receive it (Isaiah 44:3; Ezekiel 36:27; Zechariah 12:10; John 7:38, 39; Acts 1:5; 2:17, 18, 33). That is why those who receive such "oil" demonstrate their faith in it by drinking of it (by means of wine in representation of the "blood" of the Holy One of Israel, JAHESHUA MISCHAJAH, who is the Holy Spirit and Son and Christ (chosen/anointed) of God... which blood he received from HIS God and Father, the Most Holy One of Israel, JAH of Armies).
For those who NOT christians, the same can apply: they need only firmly and confidently oppose the voice... and it will go away. Problem is, most don't/won't. Rather, they "fear" such voices (and their sources)... and ultimately succumb. To the dishonor of and reproach upon the Most Holy One of Israel. But, then, that is the very PURPOSE of those voices... and goal of those whose voices make such directions. Flip Wilson's old line, "The Devil made me do it," notwithstanding, MOST ignorantly, falsely, and/or lyingly blame God, the Most Holy One of Israel, JAH of Armies. For the voice... and the resultant tragedies. I ask you, what is the BEST way to undermind someone's reputation? Is it not to lie on/about them, or do horrible things either in their name or just outright blame them for it?
It is not the voice of God who tells people to do such terrible things. That is lie... and it is perpetuated by the father of the lie, earthling man's adversary, the one called "Satan" and "Devil."
Again, I bid you peace.
A slave of Christ,