Jesus is speaking in John 12:24 when he gave this metaphor from our world of nature.
Truly I tell you, unless a grain of wheat falls to the ground and dies, it remains by itself. But if it dies, it produces a lot of fruit. (CSB)
Death must take place before there can be life. If you place a seed in the ground, it will die. But in time, if you watch the place of death, you will see a small green shoot appear; then a plant emerging from the ground; then the ear; and finally, the harvest. If the seed does not die, there can be no harvest.
So, what does Jesus mean? He was referring to himself and his own death. His life was the seed that had to be planted. Unless he went to the cross and was willing to die, his whole purpose in coming to earth would have been wasted. But if it were put in the ground (and it was), it would bring forth much fruit.
Being a Christian involves dying to self. You do not become a follower of Jesus by doing virtuous deeds, or any deeds. There is one thing and only one thing you must do: come to the cross and die to yourself. There is no other gospel. That is the great Christian paradox: the only way to have life is to lose it, to put an end to our own efforts to save yourself and accept his death.