'Sincere' in the Bible

Give sincere homage! Otherwise he will be angry, and you will die because of your behavior, when his anger quickly ignites. How blessed are all who take shelter in him!

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.

I will praise You with a sincere heartwhen I learn Your righteous judgments.

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