Definition: Not yielding the desired outcome; fruitless; lacking substance or worth.
Not obtaining the desired result is most disappointing.
This is especially true when it involves one's worship.
That is why it is so important to make sure one's worship is not in vain.
Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand,by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain.
1 Corinthians 15:1-2
"Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven; but he who does the will of My Father who is in heaven."
"This people honors me with their lips, but their heart is far away from me. But in vain do they worship me, teaching as doctrines the precepts of men."
"If anyone thinks himself to be religious, and yet does not bridle his tongue but deceives his own heart, this man's religion is worthless."
"If I speak with the tongues of men and of angels, but do not have love, I have become a noisy gong or a clanging cymbal. And if I have the gift of prophecy, and know all mysteries and all knowledge; and if I have all faith, so as to remove mountains, but do not have love, I am nothing. And if I give all my possessions to feed the poor, and if I deliver my body to be burned, but do not have love, it profits me nothing."
1 Corinthians 13:1-3