Matthew 5:48 is not about keeping His commandments and you know it. It is about a person being perfect by doing good to his enemy, just as God does good things to the evil.
If you want to make up a story that it is talking about keeping His commandments perfectly, then I'll play along. You have to believe perfectly and have perfect faith to be saved. Since you don't believe perfectly all the time, you can't be saved by your imperfect faith.
Oh, and you must have the perfect interpretation of all the Bible, and pray perfectly, and worship perfectly, and say everything perfectly, and find the perfect church to attend, or else it's the lake of fire for you.
Remember, you are the one who referred to Matthew 5:48. So, if you aren't perfect, justbyfaith, you are doomed. It's the end for you; there is no hope unless you are perfect as the Heavenly Father is perfect.
Don't you like that? Is that what you mean, when you say keep His commandments perfectly? Don't you actually mean do all things, say all things, and think all things perfectly? So, have you been perfect today? yesterday? how about tomorrow, think you will be perfect?