Hi Light,
That makes perfect sense to me in the context you just mentioned.

Thanks for restating, but you don’t need to provide a page number, now that we know the source and the meaning.
Maybe for others’ sake, it might be good to post what Teresa wrote of union in the 5th mansion, that is attained
without contemplative gifts from God.
Despite all I have said, this Mansion seems to me a little obscure. There is a great deal to be gained by entering it, and those from whom the Lord withholds such supernatural gifts will do well to feel that they are not without hope; for true union can quite well be achieved, with the favour of Our Lord, if we endeavour to attain it by not following our own will but submitting it to whatever is the will of God. Oh, how many of us there are who say we do this and think we want nothing else, and would die for this truth, as I believe I have said! For I tell you, and I shall often repeat this, that when you have obtained this favour from the Lord, you need not strive for that other delectable union which has been described, [she’s speaking of the supernatural *prayer of union]
for the most valuable thing about it is that it proceeds from this union which I am now describing; and we cannot attain to the heights I have spoken of if we are not sure that we have the union in which we resign our wills to the will of God.
I have said a great deal about this elsewhere, sisters, because I know that, if we were to fail here, we should be lost.
May the Lord grant us never to fail, and, if that is to be so, I tell you that you must not cease to beg His Majesty for the
union which I have described. It may be that you have experienced devotion and consolations, so that you think you have reached this stage, and even enjoyed some brief period of suspension in the Prayer of Quiet, which some people always take to mean that everything is accomplished. But, believe me, if you find you are lacking in this virtue, you have not yet attained union.
So ask Our Lord to grant you this perfect love for your neighbour, and allow His Majesty to work, and, if you use your best endeavours and strive after this in every way that you can, He will give you more even than you can desire.
catholictreasury.info/InteriorCastle/ic15.htm
Just to clarify, this is not describing the
transforming union of spiritual marriage.