From time to time I pop into my Superannuation account to see how things are tracking. For a long time I couldn't put much in there and... yeah... But 'amazingly', when I make deposits, the amount of return I earn increases. Who'd have guessed?
It's a universal principle: what we invest in, we get a dividend from.
Gal. 6:6 "Let the one who is taught the word share all his good things with the teacher. 7 Don’t be deceived: God is not mocked. For whatever a person sows he will also reap, 8 because the one who sows to his flesh will reap destruction from the flesh, but the one who sows to the Spirit will reap eternal life from the Spirit. 9 Let us not get tired of doing good, for we will reap at the proper time if we don’t give up. 10 Therefore, as we have opportunity, let us work for the good of all, especially for those who belong to the household of faith."
Paul puts it, "You reap what you sow." You get out what you put in. Entry to the Christian life is free in Jesus, but if we want to reap all the benefits of that life, we have to invest in it. Paul says that the difference between sowing into the flesh and sowing into the Spirit is doing good. The fallen flesh can only grow destruction, but the life of the Spirit grows eternal life.
So how do we sow into the things of the Spirit? Paul says that the one taught should share every good thing with their teacher. In other words, we sow into good teaching. What happens when we do that? We're strengthened against being led astray, and grow in our understanding of God. We also sow into good works. This isn't about earning our salvation (we already have this), it's about reaping good by sowing good.
Put it this way... have you noticed how positive people tend to attract people? We love being around people who love. They reap what they sow. But bitter people drive others away and tend to attract more bitterness and evil. People who sow into the things of God through prayer, Bible engagement, and fellowship, become more spiritual. Those who neglect these things don't. In fact, they often become more worldly.
You reap what you sow. So what are you hoping to reap? Sow into that!