"And the LORD spake unto Moses, saying, Command the children of Israel, that they put out of the camp every leper, and every one that hath an issue, and whosoever is defiled by the dead: Both male and female shall ye put out, without the camp shall ye put them; that they defile not their camps, in the midst whereof I dwell. And the children of Israel did so, and put them out without the camp: as the LORD spake unto Moses, so did the children of Israel." (Numbers 5:1-4)
This commandment seems very harsh when we first encounter it. Diseases such as leprosy and issues, and defilement by contact with a dead body were, and still are, a part of everyday life; although because of the benefits of science those of us fortunate enough to live in an industrial society don't experience severe disease and death as frequently as even our grandparents did.
There is ample reason why this commandment was given and it is easily understood. Just think of leprosy for a moment. This used to be a severely debilitating disease, often leading to the death of the sufferer. Now, thanks to modern antibiotics this feared disease does not pose the threat that it used to in the Middle East. The commandment therefore was to prevent the spread of this contagious disease, and the same would apply to the other condition mentioned in this commandment, that of issues, and to a lesser degree dead bodies that may carry a communicable infection.
But as well as being laws designed to enforce public health there are also spiritual lessons to be gained from understanding this commandment, but which the Israelites failed to appreciate. We therefore must ensure that we do not fellowship doctrinal error otherwise we will suffer the same fate as those who own the lie.As Paul says in Romans 10 "For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God". They saw the law as something to be obeyed to the letter and not as a "school master". They could not see that leprosy was a symbol used of sin, and that this as a contagious disease spread by contact, ultimately leading to death, a very apt symbol of sin and having the same consequences. This was the real lesson of the commandment, that contact with sin defiles the individual as well as those they subsequently come into personal contact with and having the same final outcome.
Some deny this principle, saying that "guilt by association" (their description) is unscriptural and our immediate reaction is that they are right for Yahweh does not hold one individual guilty of another's sin. Yet, if we consider this for a moment there are examples in scripture where this does not seem to apply. Take, for instance, Numbers 16:26 "And he [Moses] spake unto the congregation, saying, Depart, I pray you, from the tents of these wicked men, and touch nothing of theirs, lest ye be consumed in all their sins". So we see that the sin remained "theirs" i.e. Korah's, Datham's and Abiram's yet those who associated themselves with these evil men would also suffer because they condoned "their" sin, though not guilty of it themselves.
What is an extremely well founded principle of God's Word, and which this is but an example taken from many instances, is "defilement by contact" and this is a much better explanation of the principle that Yahweh applies, and can be summarised in "For he that biddeth him God speed is partaker of his evil deeds" (2 John 1:11). Therefore, a fellowshipper or partaker of another's evil deeds will suffer a similar fate to the one who owns the evil deeds. We therefore must ensure that we do not fellowship doctrinal error otherwise we will suffer the same fate as those who own the lie. Under these circumstances our sins are not preserving God's Truth and not loving the brother or sister, but leaving them to the consequences of their error; this is why we will be held responsible and suffer for it.