David put it like this:
"But who am I, and what is my people, that we should be able to offer so willingly like this? for all things come from you, and from your own riches have we given you."
and Paul said, "as God has prospered him..."
When I give, it's because He gave, and gave freely. The gifts of God are many indeed, and focusing on them is the way to the true enjoyment of life.
Of course, His greatest gift is His love, which is epitomized in the Person of His Son, given that we should not perish:
"God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have everlasting life."
Now, if you say, "I know all this," you're missing the point. It's not in knowing these things that they help us, and refocus our lives, but in actually thinking this way all the time, and meditating on the goodness of God that will help us be filled with joy in our daily lives. In a few minutes, I'm going to eat breakfast, made from food that there was money to buy. I slept last night in a nice bed, and I got rest. Most of all, however, I'm enjoying the beautiful morning that He gave me. The sun rose over a town that had a bit of rain last night, and the air is fresh and the day is beautiful.
I need to think like that all the time. So do you.
A grateful heart toward God is at the root of all our joy.