What is spiritually fit?

Just as with becoming physically fit, to become spiritually fit we also have to "exercise."

The Bible mentions that we have to "exercise faith." (John 3:16) Which involves more that just "having" faith.

Throughout James chapter 2, the point is emphasized that faith without works is dead. Verses 20 & 26 in particular say: "Do you care to know that faith apart from works is inactive? Indeed as the body without spirit is dead, so also faith without works is dead."

These works involve following God's commandments. Worshiping him the way HE outlines for us in The Bible. Jesus said the greatest commandment is to "love Jehovah your God with your whole heart and with your whole soul and with your whole mind." (Matthew 22:36) And 1 John 5:3 clearly shows what following that commandment means for us: "For this is what the love of God means, that we observe his commandments."

In the book of Hebrews Paul said "those who through use have their perceptive powers trained to distinguish both right and wrong." (Hebrews 5:14) The Greek Word used for trained literally means having been trained (like a gymnast).

So just like an athlete vigorously trains to become fit and prepared, we spiritually become fit or mature, when we take in accurate knowledge and exercise our thinking ability to distinguish right from wrong from God's standpoint.