Herod had John beheaded to keep a promise.是什么意思？

Herod had John beheaded to keep a promise.

希律为了守所起的誓把约翰斩头.

Herod

n. 希律王（约公元前73-公元前4）；

例句
King Herod found no cause in this man.
希律王在这人身上找不到理由判他罪.

had

v. 有（ have的过去式和过去分词 ），（亲属关系中）接受，拿，买到；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

John

n. 茅房，厕所；

例句
He was appointed Apostolic Administrator of Minsk by Pope John Paul II.
他被教皇约翰·保罗二世任命为明斯克区的宗座署理。

beheaded

v. 砍（某人的）头，砍头处决( behead的过去式和过去分词 )；

例句
Charles I was beheaded by the Cromwellians.
查理一世被克伦威尔派斩首。

to

prep. 向，朝着，到，关于，属于；adv. 朝一个方向的，到某种状态，关闭；

例句
I suggest you leave it to an expert...
我建议你把它留给专家来解决。

keep

vt. 保持，保留，遵守，阻止；vi. （食品）保持新，保持健康；n. 保持，保养，供养，抚养，生活，生计，饲料；牧草；

例句
The company say they're able to keep pricing competitive...
该公司说他们能够使定价保持竞争力。

promise

vt. 允诺，许诺，给人以…的指望或希望，保证；vi. 许诺，有指望，有前途；n. 许诺，希望，指望，允诺的东西；

例句
I'm not impressed by the promise of tax cuts against the backcloth of a public-spending deficit.
在公共开支出现赤字的情况下承诺减税让我不以为然。