Jesus is not saying that he'd rather we have cold faith or that our love be cold, instead of being lukewarm. No Father wishes that his children are cold in their hearts toward him.
Think of the attributes of hot and cold.
Hot:
Healing - hot compresses, baths and heating pads are used to bring healing to sore muscles.
Comfort - hot drinks and sitting by a fire brings comfort on cold winter nights.
Cold:
Healing - ice and cold compresses are used on sprains and sore muscles to bring down swelling and help heal.
Refreshing - ice cold drinks and dips in cold pools refresh us on hot days.
Hot and cold both bring healing, while one also refreshes and the other comforts. Lukewarmness does neither. It cannot refresh, comfort, or heal. Lukewarmness is good for nothing. Jesus is saying we need to be people who bring healing, comfort, and refreshing into other's lives. Hot and cold are both good in His eyes. These are the deeds that He's looking for in His children.
Artwork: Ice and Fire, unknown
