'Pure Heart' in the Bible

All these, being men of war able to order the array, came to Hebron with pure heart, to make David king upon all Israel. And thereto all the rest of Israel was of one accord to make David king.

And thou, Solomon my son: know God thy father and serve him with a pure heart and lust of soul. For the LORD searcheth all hearts and understandeth all the imaginations of thoughts. If thou shalt seek him, he will be found of thee: But and if thou forsake him, he will cast thee off forever.

And the people rejoiced that they were so willing: for with a pure heart they were willing unto the LORD. And thereto David the king rejoiced with great gladness.

And give unto Solomon my son, a pure heart to keep thy commandments, thy testimonies and thine ordinances, and to do all, and to build the house which I intended."