As Paul writes this, these were not to be momentary attitudes but continuous states. This is what is developed and produced in us by God's Spirit because of the relationship with Christ. Thus, when he says "watch," he is not speaking about an occasional absence of sleep but a determined effort at vigilance so that our spiritual liberty will not be endangered by compromise with anything in our environment.
It means not playing with temptations. He is telling us to be stable, not to be flitting from one fad and fashion to another like the people in this book were doing. He tells them, "Be like men," meaning, "Be mature, stable, responsible to duty." He wants us to understand that nothing fine and good can be built if it is treated in a casual, informal, easygoing manner.
Paul wants us to understand that being strong in God is not something inherent within us. It does not come naturally. Human nature is at war against God. It resists seeking Him. Being strong in God is derived from the relationship with Him, and this relationship must be worked on, even as a good relationship with another human being must be worked on.
Finally, he speaks of love, the love of God. This is not a syrupy affection with a lot of hugs, charm, or social graces, though it may include those things. The Bible, in fact, says that "charm is deceitful and beauty is vain." He is not saying that they are evil but that they have the power to deceive people into thinking that, because one is charming or beautiful, he is somehow converted. He is warning us that those things might be nothing more than a carnal façade.
What is love? Love is doing what is right from God's perspective. Remember, this is the same apostle who admonishes Timothy to rebuke people before all—even right before the entire congregation. If that is what it took to turn a person back to God, that was what was to be done, and it was an act of love. Love is being responsible, honest, loyal, trustworthy, faithful. Love is being zealous toward God, and it is many other things as well.