'Sincere' in the Bible

For their heart was not steadfast toward Him,Nor were they faithful to His covenant.

How blessed and favored by God are those whose way is blameless [those with personal integrity, the upright, the guileless],Who walk in the law [and who are guided by the precepts and revealed will] of the Lord.

May my heart be blameless in Your statutes,So that I will not be ashamed.