I know of people who practice meditation, hoping to achieve some sort of nirvana or enlightenment. This is playing a dangerous game because you don't know what you can get yourself into. Unknown spirits are legion out there, ready to enter your life. This I can personally testify. Then you can meditate like that for many years and realize nothing extraordinary, and whatever you might realize still turns out to be your own thoughts. Meditating upon the Lord is totally different. For one thing, you already know who he is, the only true holy God. The other thing is that you don't have to strive hard in any way, hoping to receive wisdom or illumination. On the contrary, you only need to be receptive to his word and rest passively in him at all times. Then he'll reveal all you need to know for your salvation. This is spontaneous, effortless learning, opposite to how we learn things in the world. This is how how we can achieve union with the Lord with the aid of the Holy Eucharist. To be of one heart and one mind with the Lord is our ultimate fulfillment on earth.