Here I will give an answer to your question as Vaishnavas tend to do.
First of all, a Vaishnava does not take any food just like that, just to take it and begins to eat, but he takes a food with the intention that he will offer it first to the Lord Krishna. Basically there are two main reasons for that:
1) One reason is that the Lord asks to be offered the food before we eat it. This is nicely seen from the Bhagavad gita 9.26:
"If one offers Me with love and devotion a leaf, a flower, fruit or
water, I will accept it."
See, Lord Krishna does not think that we should take and eat some food if we have not first offered it to Him! In fact He specifically says that we should offer food to Him with love and devotion (bhaktyā, bhakti-upahṛtam). The idea is that we offer food to Him with an attitude like that we serve some great and important exalted guest -- a guest who will accept our offering, as He says "I will accept it". It is a kind of service that we offer for His satisfaction, but it is also the way of developing a relationship with Him, giving with devotion (bhakti) -- accepting.
Then the Lord takes the food and it is considered that the food is left for us to eat it and venerate (regard with great respect; revere), as if that were food remnants that are left over after the Lord took the food. Those remnants are called the Lord's prasāda "mercy".
2) And secondly there are karmic reasons. It is said in the Bhagavad gita 3.13:
"The devotees of the Lord are released from all kinds of sins because
they eat food which is offered first for sacrifice. Others, who
prepare food for personal sense enjoyment, verily eat only sin."
Here it is said that offering the food to the Lord is, like, a participation in the sacrifice, and because of this sacrifice the food is free of sin.
So, first we offer Him food in sacrifice and then partake of the remnants that are literally called His prasāda "mercy".
Thus you can meditate on all of that mentioned above when you offer the food and later when you eat the food you can appreciate and enjoy the Lord's remnants, the Lord's prasāda "mercy", and thus you can venerate.