A brother comes up to you and says... "The bible says that as a man thinketh so is he.... I was reading this today and I believe that what the Spirit is saying is that if we think successful thoughts we will ultimately do those things that make us successful. If we think negative thoughts about ourselves we will do things that make us unsuccessful." Now you might say "My spirit bears witness that that is true" I think you are understanding that scripture correctly.
But let us look at the passage referenced and see if that is what the Spirit is saying.
1When thou sittest to eat with a ruler, consider diligently what
is before thee:
2And put a knife to thy throat, if thou
be a man given to appetite.
3Be not desirous of his dainties: for they
are deceitful meat.
4Labour not to be rich: cease from thine own wisdom.
5Wilt thou set thine eyes upon that which is not? for
riches certainly make themselves wings; they fly away as an eagle toward heaven.
6Eat thou not the bread of
him that hath an evil eye, neither desire thou his dainty meats:
7For as he thinketh in his heart, so
is he: Eat and drink, saith he to thee; but his heart
is not with thee.
8The morsel
which thou hast eaten shalt thou vomit up, and lose thy sweet words.
We can now see from the rule of context that the ruler who is offering the dainties is speaking hospitality and pretending to be nice but has negative plans for his guest.. "As he thinks in his heart, so is he" the real and evil motives is who the ruler really is, not this hospital person he is pretending on the outside to others to be"
Now that is a powerful sermon that NEEDS to be preached and IS what the Spirit intended this verse to be used to preached. But because of ignoring context many are quoting and using this half verse to teach a message that might be helpful in the sense that it is indeed important to not be negative, but this is not the message that the Spirit intended for this verse.
It is not about winning an argument it is about receiving the HOLY SPIRIT INSPIRED UNDERSTANDING That GOD intended and that Solomon meant when he wrote it.
Your spirit will bear witness that the context says it is about the ruler thinking evil thoughts in his heart toward his guest and that is who the ruler really is. If not, you are going to have to explain why.