The idea of the reproductive system is not a far stretch to make, since the parable is speaking of reproduction- A seed carries the DNA for the next generation of plant. The cycle is -seed which is planted, germination, growth, fruit production, seed, and in all cases death sometime comes to the plant, some plants have many reproductive cycles, some only one. The point of faith is to produce fruit, which bears the seeds that will become the next generation of faith. It is very much about reproduction, and thus not at all a stretch to correlate it to human reproduction, Paul himself does so, when he calls some of the "brethren" ---"Infants" or "babes". John calls some of his followers "little children". Paul as well to the Corinthians calls himself their father, he also says to the Galatians :
19 My children, with whom I am again in labor until Christ is formed in you—
He speaks in terms of human reproduction. Christ Himself says we "must be born again". Indeed Peter correlates the "seed" with human reproduction as well:
1 Peter 1:23
23 for you have been born again not of seed which is perishable but imperishable, that is, through the living and enduring word of God.
Is not the term "born again" analogous to human reproduction?
Yes I agree that it is not what the parable is speaking of, it is my own correlation which I believe works to help explain it.
Also you say that Christ is the sower and that is true, He was, but those who believe also become sowers- Paul says that he planted and Apollos watered- but God caused the increase. (1 Cor 3:6). That is my point- God causes the increase, we ourselves do not, but the condition of our soil, how we respond to Him, has direct effect on whether or not that growth happens. If we respond correctly then He will cause the growth. Also we as believers can help others to respond correctly, we can encourage them to repent of sin, we can pray for and with them, we can walk beside them and help them up when they stumble, exhorting them when necessary.
Scripture is pretty clear
1 Corinthians 6:9-10
9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals,
10 nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God.
18 But if you are led by the Spirit, you are not under the Law.
19 Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality,
20 idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions,
21 envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God.
22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness,
23 gentleness, self-control; against such things there is no law.
24 Now those who belong to Christ Jesus have crucified the flesh with its passions and desires.
25 If we live by the Spirit, let us also walk by the Spirit.
The key is what is our practice? What is the produce of our life? Do we produce the fruits of the flesh or the fruits of the Spirit? What is our occupation? Peter says that:
2 Peter 1:5-11
5 Now for this very reason also, applying all diligence, in your faith supply moral excellence, and in your moral excellence, knowledge,
6 and in your knowledge, self-control, and in your self-control, perseverance, and in your perseverance, godliness,
7 and in your godliness, brotherly kindness, and in your brotherly kindness, love.
8 For if these qualities are yours and are increasing, they render you neither useless nor unfruitful in the true knowledge of our Lord Jesus Christ.
9 For he who lacks these qualities is blind or short-sighted, having forgotten his purification from his former sins.
10 Therefore, brethren, be all the more diligent to make certain about His calling and choosing you; for as long as you practice these things, you will never stumble;
11 for in this way the entrance into the eternal kingdom of our Lord and Savior Jesus Christ will be abundantly supplied to you.
he says that if these qualities (the divine nature supplied by God through the Holy Spirit) are ours and are increasing, then we will be fruitful, we will grow to maturity. But the one who lacks the divine nature has forgotten his purification from sin. So here we see that someone can know of their purification from sin and forget about it. But as long as we nurture our faith with the divine nature we are assured of salvation, in other words we have to respond as "good soil".
James also says:
22 But prove yourselves doers of the word, and not merely hearers who delude themselves.
23 For if anyone is a hearer of the word and not a doer, he is like a man who looks at his natural face in a mirror;
24 for once he has looked at himself and gone away, he has immediately forgotten what kind of person he was.
25 But one who looks intently at the perfect law, the law of liberty, and abides by it, not having become a forgetful hearer but an effectual doer, this man will be blessed in what he does.
Hearing and knowing is not what saves us- it is responding to the word of God in our lives, walking by the Spirit. We do not do so perfectly, but with "practice" we get better at it- this is the process of sanctification or Christian growth.
If someone claims to be a follower of Christ and yet remains a practicing homosexual, or adulterer, or idol worshiper, etc... they are merely hearers and not doers. But we can come alongside them and remind them of their purification from sin, and admonish them to repent of sin, and in this way we cultivate their soil, so that the seed has a better chance to continue growing. That is what Paul constantly did in his letters to the churches- He labored over them so that Christ might be formed in them. He cultivated their soil so that the seed of God's word might bear fruit. The fruit of salvation- the fruits of the Holy Spirit, the divine nature of Christ in us, so that they can go on to scatter the seeds of their fruit (the gospel) on the soil of those whose lives they touch.