What is acceptable worship?

Hebrews 12:28 says "Since we are receiving a kingdom which cannot be shaken, Let us worship God acceptably with reverence and awe for our God is a Consuming Fire." Still on the subject of worship a recent journal discussed the point that if there is acceptable worship then there is also unacceptable worship. What is acceptable worship? The first portrait of worship casts Cain and Able, the sons of Adam and Eve. Cain was a gardener, botonist, a man of the soil; Abel was a shepherd, a man of the flocks. The time comes when they both bring their sacrifices to the Lord, but only Abel’s was pleasing to the Lord, or acceptable. Why? Remember, what Cain brought to the Lord was a beautiful offering of fruit from the ground, most likely with a proud smile on his face, expecting to impress the Lord with his succulent sacrifice. He’d harvested the fruit, tilled the land, nourished the seeds, and now was presenting an impressive buffet to God! Abel brought to the Lord one of his innocent baby lambs. Undoubtedly with tears in his eyes and hurt in his heart, after having to slit the throat of one of his beloved flock. Both were costly sacrifices, but the approaches were polar opposites: Cain went to God with pride in his heart; Abel went with brokenness. Abel's sacrifice was pleasing to the Lord, because it was obedient to God’s design.