Bismillah
as salam alykom Shamms,
You asked a very good question:
Isn't this verse giving men permission to approach the women they possess (wives, slaves, sisters, mothers) when and how they see fit?
In fact this Ayah instructs to totally the opposite demonstrating how Islam does not overlook the tiniest details. It is the Ayah regulating the intimate relation between spouses. It shows how Allah Tackled each and every aspect of our lives, special intimate relation but in a very modest and polite manner, avoiding obscene expressions,yet very clear and direct about how a man should approach his wife.
Allah Used nesaukum, which is translated as your women=your wives.
Your wives are as a tilth unto you; so approach your tilth when or how ye will
In Arabic, the Ayah says: anna shetum=as you please or as you wish. This Ayah had been revealed in an occaision when Al Ansaar (Medina people who vowed to support and accomodate the Messenger blessing and peace be upon him) came inquiring to the Messenger blessing and peace be upon him about the positions they may apply during the intimate relation. They asked him saying that Jews told them, if they approached their wives while laying on their sides, the potnetially conceived child would come with twised eye balls. Thus, the Messenger blessing and peace be upon him explained that they are allowed to enjoy their spouses on any position, provided they use the legitimate point (in Islam anus sex is illgitimate). That is why Allah referred to this point politely saying tilth. Tilth is an implication of sawing seed that would grow. Using the proper point is means to conceive children which is the main reason of marriage and forming families. The Ayah also teaches men how not to just throw themselves on women without any introduction or helping her to prepare. This is what the Ayah is about. It is one of the most delicate Ayahs that sets forth rulings on the intimate relation between spouses and yet maintaining modesty and polite wording in an incomparable manner.
but do some good act for your souls beforehand
This is the part of the Aya I am speaking about, with all due resepct to the translator, he did not cover all of it. In Arabic, it says: qademou le anfusikum. It means make introductions to yourselves. It has a double fold meaning. As I explained above. Prepare the women, make some introduction to yourself before you start the actual act, and also, pronounce the invocation taught by the Messenger blessing and peace be upon him in order to protect both you and your wife from interception of the devil.
In sha Allah I answered your question Shamms and Allah Knows best.