Why

2 Samuel 21:2
At this, David summoned the Gibeonites and spoke to them. (Now the Gibeonites were not Israelites, but a remnant of the Amorites. The Israelites had taken an oath concerning them, but in his zeal for Israel and Judah, Saul had sought to kill them.)

Ezekiel 17:18, 19
He despised the oath by breaking the covenant. Seeing that he gave his hand in pledge yet did all these, he will not escape!' . . .

commandment

2 Chronicles 30:12
Also, the power of God was on the people in Judah to give them one heart to obey the command of the king and his officials according to the word of the LORD.

Ecclesiastes 8:2
Keep the king's command, I say, because of your oath before God.

Romans 13:5
Therefore, it is necessary to submit to authority, not only to avoid punishment, but also as a matter of conscience.