In 1 Corinthians 15, Paul writes that all who are in Adam die, and all who are in Christ live. We need to sow the seed that needs to die in order that the body God planned can grow (15:22, 36, 38). Is it correct to say that our physical body is the seed, and this earth (planet Earth!) is that in which we are buried? Just like the caterpillar that becomes a butterfly, we need to develop our spiritual body that is imperishable. We are made of dust, and God breathed life into us. We need to repent and be baptized to receive the Spirit. That way we become like the man from heaven (15:48). If we do not accept Christ, we did not develop spiritual body (15:44). That would refer to the ones that love their life, and therefore destroy it (John 12:25). They want to stay as seed... Is this understanding correct? -- Tomislav Zrinksi
The spiritual body is our body after it is transformed at the last day. Until then, we have only the fleshly body. Not that some of your ideas find no biblical support, but the term as Paul uses it in 1 Corinthians 15 refers to something different.
Our bodies are indeed "sown" into the earth, but this is at the time we die. They do not automatically germinate into spiritual bodies--Paul is only developing an illustration here--but when they are resurrected, at the last trumpet, the transformation takes place.
On the other hand, it is true that we, like seeds, are to die to self (John 12:23-26. See 1 Peter 2:24; Colossians 1:22, 2:20, 3:3; Galatians 2:20, 5:24, 6:14; Romans 6; etc). In that sense, yes, we are to develop spiritually. But, once again, I do not think this is what Paul has in mind in 1 Corinthians 15.