Be perfect, therefore, even as your heavenly Father is perfect. Matthew 5:48
It is a given that we as humans cannot achieve what Jesus says. It is an impossibility for us to completely be like God.
We cannot be all knowing.
We cannot be all powerful.
We cannot love unconditionally--perhaps at moment, but not totally.
We cannot achieve perfection in our relationships.
We simply cannot do it.
This is why we have the concept of grace. This is why St. Paul penned the words in Romans 3:
For there is no distinction, 23since all have sinned and fall short of the glory of God; 24they are now justified by his grace as a gift, through the redemption that is in Christ Jesus, 25whom God put forward as a sacrifice of atonement by his blood, effective through faith.
We are not saved/justified/made right with God by any of our actions. We are only made right with God by Him through Christ. Period. End of story.
Which, of course, then leads to the question: why try to achieve perfection at all? If perfection doesn't save me and I cannot attain it, why should I even go there? Why should I even strive for it? Why apply myself toward something that is an impossibility? Why try when failure is the outcome?
Many times I have sought a good argument for these questions. Many times, I have preached arguments, that I believe fell short. But I think I've got one now--drawn from the world of athletics.
Should a baseball player cease trying to hit the ball because his chances of actually getting a hit are generally less than 1 in 3?
Should a pitcher cease to pitch because of the rarity of throwing a perfect game?
Should a basketball player stop shooting the ball because the odds of making it are generally less than 1 in 2?
Should a football team's offense cease trying hard every play because the odds are short that they will score a touchdown on that given play?
Should a bowler cease bowling because of the difficulty in throwing a 300 game?
Should a golfer stop golfing because of the rarity of a hole in one?
Most would say that stopping would be asinine. You don't play sports because you can achieve perfection!
You also don't practice Christianity because you can achieve perfection.
You also practice and dedicate yourself and work hard in sports training your body to do better. The more reps you spend in a batting cage, the better chance you will have to hit the ball. The more times you practice shooting a basketball, the better you get at making baskets. The more you practice running a particular play in football, the more you maximize your chances of scoring a touchdown when you run it. The more you practice golfing and tweaking your swing, the more you maximize your chances of making a hole in one.
The goal drives what you do. If your goal is to hit every shot in basketball, you will work hard at achieving it--even though it is a statistical impossibility. If your goal is to get a hit in every at bat, you will work to achieve it--even though it is very, very unlikely. And so on, and so forth.
The goal in Christianity drives what we do as well. Not because we will achieve it. Not because we will achieve salvation, but because this is what it means to love God and our neighbor. Perfection is the goal, and it is our desire to achieve it--even though it is an impossibility.
But every once in a while, we hit a home run, score a touchdown, sink a hole in one, and bowl a strike. It helps us enjoy the game/life/faith, and inspires us to keep trying.