Jesus used parables to relate Heavenly truths to people in simple terms. Jesus used planting and seeds to convey Heavenly truths in Matthew 13.
In verses 3-23 Jesus tells the Parable of the sower and the seed. The sower sows the seed and it grows or dies based on the quality of the soil on which it falls. In Luke 8:11 Jesus tells us the key to this parable is that the seed is the word of God. I see two main truths we can learn in this passage. As sowers of the word, we can only spread the word and we cannot determine the harvest. As receives of the word, we must examine our souls to see that we are fertile ground for God's word to grow.
In verses 24-30, Jesus use wheat and tare to compare the lost and saved. Jesus taught that both the lost and saved are planted in this earth. They will live this earth until the time that the planter gathers the wheat into the barn. He taught that we cannot judge who is saved or lost until that time of separation.
In v31-32- - Jesus compares the kingdom of heaven to a mustard seed, which is small when planted but grows into a great tree. We see that salvation comes through One (Christ) and is spread to all who will receive.
Matthew 17:20 - Jesus says if we have faith like a mustard seed we can move mountains. A great truth we see is that as a seed must be planted to grow so faith must be acted upon to achieve miracles.
Some other thoughts
1# - You reap what you sow. (Galatians 6:7)
2# - You reap more then you sow. (2 Corinthians 9:6)
3# - You reap after you sow. (Psalms 126:5)
4# - Reaping and sowing take time and hard work. (Psalms 126:5)