Spiritual. If you claim to be "spiritual", then it seems necessary, crucial, you are acknowledging an intelligence, a power and authority greater than yourself. However, if you are claiming spiritual -and- claiming believe in yourself, are you then trying to claim you are God? 
I think when people say "believe in yourself," they are trying to believe and to declare they are capable in the activity they're trying to do, whatever that activity is.

Jesus said, "you cannot make one hair white or black,"
‭Matthew 5:36 NASB1995‬
[36] Nor shall you make an oath by your head, for you cannot make one hair white or black. 

https://bible.com/bible/100/mat.5.36.NASB1995


‭Matthew 6:27 NASB1995‬
[27] And who of you by being worried can add a single hour to his life? 

https://bible.com/bible/100/mat.6.27.NASB1995

The implication is, "If you cannot do such a simple thing, how can you do other difficult things?"

Look at God early on with Moses:

‭Exodus 4:1-8 NASB1995‬
[1] Then Moses said, “What if they will not believe me or listen to what I say? For they may say, ‘The Lord has not appeared to you.’ ” [2] The Lord said to him, “What is that in your hand?” And he said, “A staff.” [3] Then He said, “Throw it on the ground.” So he threw it on the ground, and it became a serpent; and Moses fled from it. [4] But the Lord said to Moses, “Stretch out your hand and grasp it by its tail”—so he stretched out his hand and caught it, and it became a staff in his hand— [5] “that they may believe that the Lord, the God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has appeared to you.” [6] The Lord furthermore said to him, “Now put your hand into your bosom.” So he put his hand into his bosom, and when he took it out, behold, his hand was leprous like snow. [7] Then He said, “Put your hand into your bosom again.” So he put his hand into his bosom again, and when he took it out of his bosom, behold, it was restored like the rest of his flesh. [8] “If they will not believe you or heed the witness of the first sign, they may believe the witness of the last sign. 

https://bible.com/bible/100/exo.4.1-8.NASB1995

God questions Job in Job chapters 38 to 41. And if Job is such a great guy, then why would he / the writer put in this stuff into the Bible from chapters 38 to 41? God is teaching!! And yet Job was a great guy. However, God challenges Job with a bunch of very telling questions. "Where were you when ...?" Over and over and over and over, God asks these challenging questions of job and Job cannot answer. Job chooses to repent, and tells God, so God accepts Job. Job prays for his friends. God accepts Job's prayer and restores his friends, as well as restoring to Job double from all that Job has lost.

So, back to claims of spirituality: When the Bible says God is spirit, 

‭John 4:24 NASB1995‬
[24] God is spirit, and those who worship Him must worship in spirit and truth.” 

https://bible.com/bible/100/jhn.4.24.NASB1995

...then you, if you claim to be spiritual, you're claiming a connection with God, a God, the One God is who is by definition greater than you.
And how can that be done except through Jesus Christ? Accepting God, for who He is, even as Abimelech did when Abimelech spoke to him as Lord?
Abimelech appealed to God about how Abraham treated him, and God said something like, "Yes, I kept you from sinning against Me", I think is what it was. That's all in Genesis 20, a fascinating chapter on Abimelech, a Gentile king speaking with God.

Tv show quote:
Phantom 2040, S1 E16 ~1:30, 

"As long as we are alive, we will always have a future."

I find this phrase actually profound, and I think accurate, in the context of spiritual with physical life, as Jesus Christ is risen, to live forever, to always have a future; death has no power over Him!