Psalm 37:4 gives us a precious promise of God related to the desires of our heart:
"Delight yourself also in the LORD, And He shall give you the desires of your heart."

If you want to claim this promise of God, then you must fulfill the conditions that the LORD requires for the blessing ...

According to the unchanging Spirit of Christ (Who inspired the prophet Isaiah)*, observance of the Sabbath and calling it "a delight" are  prerequisites for "delighting thyself in the LORD." and receiving the promise of Psalm 37:4:
"If thou turn away thy foot from the sabbath, from doing thy pleasure on my holy day;      and call the sabbath a delight, the holy of the LORD, honourable; and shalt honour him,      not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words:
THEN shalt thou delight thyself in the LORD; and I will cause thee to ride upon the high places of the earth, and feed thee with the heritage of Jacob thy father: for the mouth of the LORD hath spoken it." Isa 58:13-14 (KJV)

Donna Kupp

*  Here Peter shows us that the Spirit of Christ inspired the Old Testament prophets:

"Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you: Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow."  1 Peter 1:10-11