What the Bible says about Merry Heart
(From Forerunner Commentary)
Here heart and spirit are directly joined to show an effect. Merry and cheerful, both positive attitudes, are contrasted with broken and sorrow, and the effects of both are shown. Heart and spirit, then, also produce an outward effect, and they affect each other. They can be used in parallel, the one to explain the other, but they can also show their affects on each other.
John W. Ritenbaugh
The Holy Spirit and the Trinity (Part Four)