Romans 14:5
One person regards one day as better [or more important] than another, while another regards every day [the same as any other]. Let everyone be fully convinced (assured, satisfied) in his own mind.
Romans 14:23
But he who is uncertain [about eating a particular thing] is condemned if he eats, because he is not acting from faith. Whatever is not from faith is sin [whatever is done with doubt is sinful].
Romans 14:14
I know and am convinced [as one] in the Lord Jesus that nothing is unclean [ritually defiled, and unholy] in itself; but [nonetheless] it is unclean to anyone who thinks it is unclean.
1 Corinthians 8:7
However, not all [believers] have this knowledge. But some, being accustomed [throughout their lives] to [thinking of] the idol until now [as real and living], still eat food
1 Corinthians 8:11
For through your knowledge (spiritual maturity) this weak man is ruined [that is, he suffers in his spiritual life], the brother for whom Christ died.
Galatians 4:9-10
Now, however, since you have come to know [the true] God [through personal experience], or rather to be known by God, how is it that you are turning back again to the weak and worthless elemental principles [of religions and philosophies], to which you want to be enslaved all over again?
Colossians 2:16-17
Therefore let no one judge you in regard to food and drink or in regard to [the observance of] a festival or a new moon or a Sabbath day.
1 John 3:19-21
By this we will know [without any doubt] that we are of the truth, and will assure our heart and quiet our conscience before Him