We all love and expect perfection in every thing we buy, in our food, what we drive and so on, so what makes us think that God will not expect it of us when He is perfect in all He says and does? If we expect to have a right relationship with God we are not exempt from working toward that perfection. God is full of love, mercy and grace, however, His moral character puts limits on human depravity and will not abide it, which is why He says "be perfect". That is not a suggestion, it is a command.
