1 Corinthians 15:58 (NKJV)
The length of time something takes to grow is different depending on what you plant, the conditions you are growing something in, and how well you take care of what is planted. Some plants take weeks to grow while others take months before they are ready for harvest. It is not reasonable to expect every type of plant to grow at the same rate. If we understand this principle then we are able to be patient during the growth of a plant; if we don't understand it we can become impatient and give up on something that is growing and developing because we don't see the growth happening.
God has a plan for our lives and there are things He wants all of us to do, God expects us to do things that will help to build His Kingdom. But, those things we do often do not produce instant results. If we understand that in advance it makes what we do easier; we must be consistent in our work for God regardless of what results we do or do not see. We have to realize that we are dealing with eternal things and we may not see some results as fast as we like. If we are sowing the incorruptible seed of God's Word into the life of another person we can expect results.
We may work in the children's ministry at our church, or with the youth, or adults, and not see the fruit of our labors for many years. We might have the opportunity to speak to a neighbor or coworker about Jesus but that person does not receive Jesus right away. We can make investments into the lives of someone or our church today that will only bear fruit years later. But to keep on doing this we must be unmovable in our work for God. Knowing that what we do for God is never in vain helps us to do God's will regardless of any immediate results or the lack thereof.