Before anything else: God likes you just the same on the days you get it right and the days you forget. His love isn't a prize for good behavior, it's always the same size.
Have you ever been really thirsty on a hot day? The kind of thirst you get after running around in the sun. Then someone comes along and hands you a glass of nice cold water. What a relief, right? Today's verse says the person who keeps their promises is just like that, like that glass of water at just the right moment.
Imagine your friend lends you his toy and you promise to give it back tomorrow. If you give it back, just like you said you would, your friend is happy and learns something important, that he can trust you. Next time, he'll lend it to you again without worrying. That's what it means to be reliable, to be a person of your word.
But imagine you promise and don't follow through, once, twice. What happens? Your friend ends up like someone who waited for rain that never came. Little by little, he stops believing you when you promise things. Keeping your word is how you show love with action, not just with nice-sounding words.
And here's something beautiful: God is the greatest promise-keeper there is. He never fails us. When we keep our promises, we look a little bit like Him.