Is resizing a means to increasing the resolution of the image ?
Resizing can increase pixel count if you want, but in general it cannot increase the amount of detail. Though in some situations upscaling is necessary (for example, if you want to combine two images). Use Sinc (Lanczos3) interpolation when upscaling the image in Gimp.
Even more, resizing usually leads to loss of image sharpness even if you downsize the image. Some resizing algorithms are better at keeping the image sharp, but are more likely to produce resizing artifacts. Usually, you would need to sharpen (e.g. apply unsharp mask) the image after the final resize. Cubic interpolation is usually working well for downscaling.
Is it possible to increase the pixel density of the image and then resize, so that
quality of the image is not affected much?
I don't understand what you mean here.
If you mean pixel density as points per inch, and resize as an operation to change the number of pixels in the image, then you can change the pixel density freely (it affects only the size and the quality of the print), but it doesn't affect the quality of the resized image (which depends mostly on what algorithm you use to resize, whether you upscale or downscale, and how much you resize).
However, it is possible to increase the amount of detail and resolution of the image, if you have a stack of almost identical images with small shifts with respect one another. There is a technique known as super resolution. It is pretty advanced, and, as far as I know, it is not yet available in popular photographic software. But there are quite a lot of papers about it and research-grade code which can do it.