In John 6:53 Jesus said,
“Very truly I tell you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. 54 Whoever eats my flesh and drinks my blood has eternal life, and I will raise them up at the last day. 55 For my flesh is real food and my blood is real drink. 56 Whoever eats my flesh and drinks my blood remains in me, and I in them.
Towards the end of His ministry Jesus repeats Himself when He instructs his disciples regarding the Last Supper.
While they were eating, Jesus took bread, and when he had given thanks, he broke it and gave it to his disciples, saying, “Take and eat; this is my body.” 27 Then he took a cup, and when he had given thanks, he gave it to them, saying, “Drink from it, all of you. 28 This is my blood of the[a] covenant, which is poured out for many for the forgiveness of sins. 29 I tell you, I will not drink from this fruit of the vine from now on until that day when I drink it new with you in my Father’s kingdom.”
Obviously Jesus was using a metaphor to describe the tenacity one should have for seeking Him and the gifts of eternal life and Grace. We need to be like a starving person seeking food, like Esau was when he gave up his birthright for a bowl of soup, (Genesis 25:29-34). And that is what Jesus wants us to do, give up our birthwrite – the birthwrite of this world, which includes our self-interested goals and desires that this world offers. Unlike Esau who gave his birthwrite up for something worldly, Jesus wants us to give up ours for eternal life in the Kingdom.