With permission of the publisher of The Orthodox Study Bible, here is the Psalm 151.
Psalm 151 does not exist because of the different numbering system of the Psalms that occurs in the Septuagint. It occurs because it an added Psalm.
Psalm 151
1 This is a psalm written with David’s own hand, although outside the number, when he fought in single combat with Goliath
**I was small among my brothers
And the youngest in my father’s house;
I tended my father’s sheep.
2 My hands built a musical instrument;
My fingers turned a lyre.
3 And who shall tell my Lord?
The Lord Himself, He Himself hears.
4 He sent forth His Angel
And took me from my father’s sheep;
And he anointed me with his
anointing oil.
5 My brothers were handsome and tall,
But the Lord took no pleasure in them.
6 I went out to meet the foreigner,
And he cursed me with his idols;
7 But I drew his own sword and
beheaded him,
And removed disgrace from the
children of Israel.**
[And the footnote commentary;]
151 **Ps 151 is outside the number of the Psalter, but written in David’s own hand (v.1). It concerns the slaying of the giant Goliath. Historically, David slew him as recorded in 1Kg17 [which may be 1Sam outside the septuagint] . He slew him through humility. (I was small, v.1) and through the Lord (v. 3).
From a spiritual standpoint, Goliath stands for the sinful passions of arrogance and vainglory (see also Ps 143 [which is Ps 144 outside the Septuagint]). Thus, with the Lord’s help, we slay these giants with humili**ty.
Note that the spelling of “Lord” does not follow the western convention of using all capital letters as LORD. ]