Well to me the 4 of Pentacles is a very solid, stable card. Pentacles correspond with the Earth element and so are all about things on the physical plane such as money, possessions, the body, the home etc.
Four is a very solid number. When I think of the number 4 I think of things like 4 directions on a compass, 4 walls of a building. It's a number of structure, stability, boundaries, foundations etc.
Put all of this together and add the image on the card you're looking at (I'm presuming you're using a deck based on the Rider-Waite-Smith deck), so you're looking at an image of a person sitting down holding onto 4 pentacles. I've just had a look at the Moon Garden card and it does show someone with 4 Pentacles on top of him. They're stopping him from moving from what I can see.
It's about keeping what you have close to you, being possessive or just protecting what you have. It can be a card about control, especially in relationship readings. It's about being comfortable with what you have and maybe holding on a little too tightly -hence how it's often referred to as a 'miser card'.
Sometimes people get so caught up in keeping hold of what they have whether that's possessions or other people that they find that rules them and they can't move past that.
It could also be talking about simply protecting what you have. In the Thoth deck the image on the card looks a little bit like a castle so it seems more protective than possessive.
I've attached an image of the Moon Garden card.