'Onan,' as in Genesis 38, describes the evil from the falsity of evil which was later prominent among the Jewish peoples.

(Посилання: Arcana Coelestia 4837)

4837. 'And so it was, when he came [in] to his brother's wife, that he spilled it on the ground' means the reverse of conjugial love. [This is clear from the following considerations:] 'Er, Judah's firstborn' is used to describe falsity springing from evil which reigned in the Jewish nation at first, and 'Onan the secondborn' to describe evil begotten by falsity springing from evil which reigned in that nation later on. And 'Shelah the third son' is used to describe the idolatry which followed on from this and reigned in that nation at a still later time, 4826. Evil begotten by falsity springing from evil is described by the action Onan took, which was this: Being unwilling to provide seed for his brother, he spilled it on the ground. The reason this means that which is the reverse of conjugial love is that the conjugial relationship is used to mean in the internal sense that which is the essential element of the Church. Essentially the Church is a marriage of goodness and truth; and evil begotten by falsity springing from evil is the complete reverse of that marriage, that is, those with whom that kind of evil exists are the reverse of it.

[2] Nothing of true marriage meant both in a spiritual sense and in a natural one existed with that nation. This is quite evident from the fact that men were permitted to marry more than one wife; for where a marriage meant in a spiritual sense exists - that is, where the good and truth of the Church exist, consequently where the Church exists - that practice is not at all permitted. Genuine marriage cannot possibly exist except among those with whom the Lord's Church or kingdom exists, yet not with these except between pairs, 1907, 2740, 3246. The marriage of a pair in whom genuine conjugial love is present corresponds to the heavenly marriage, that is, to good and truth joined together. That is to say, the husband corresponds to good and the wife to the truth of that good. Also, when genuine conjugial love is present in them, that heavenly marriage is present too. Therefore where the Church exists men are never permitted to marry more than one wife. But because no Church existed among those descended from Jacob, only that which was a representative of the Church - that is, the external shell of the Church without its internal substance, 4307, 4500 - they were therefore permitted to have more than one. Furthermore the marriage of one husband to a number of wives would present in heaven an idea or image in which so to speak one good was joined to a number of truths which do not agree with one another, and so an image in which there was no good at all. For when its truths do not agree with one another good ceases to be good, since good receives its particular nature from truths and their agreement with one another.

[3] It would also present an image in which so to speak the Church was not one Church but many, set apart from one another along the lines of the truths of faith, that is, along doctrinal lines, when in fact the Church is one if good is the essential element there and this receives its particular nature from truths and is so to speak moderated by these. The Church is an image of heaven, because it is the Lord's kingdom on earth. Heaven consists of many distinct and separate general communities, and of smaller ones subordinate to these general ones; nevertheless good makes them a united whole. Good there enables the truths of faith to stand in agreement with one another; for these look to good and are grounded in it. If the truths of faith and not good were the lines along which parts of heaven were separated from one another, heaven would cease to be heaven, because there would not be any unanimity at all. For their oneness of life or unity in soul could not come to them from the Lord and exist among them. That oneness dwells solely within good, that is, within love to the Lord and love towards the neighbour. Love binds everyone together, and when the love of what is good and true is present in each individual, everyone shares that which comes from the Lord, so that the Lord is the One who binds everyone together. The love of what is good and true is called love towards the neighbour, for the neighbour is one with whom good and accompanying truth are present, and in the abstract sense good itself and its truth. From these considerations one may see why within the Church marriage must be a relationship involving one husband and one wife, and why the descendants of Jacob were permitted to marry more than one wife. They were permitted to do so for the reason that no Church existed among them, and therefore a representative of the Church could not be established among them by means of marriages, because the reverse of conjugial love reigned among them.