When water is placed in a water bottle, the water inside takes on the shape of the water bottle. If water is in a cup, it takes on the shape of the cup. When water is "in" something, it takes on the shape of what it is "in". When we are "in Christ", we should lose our old form and take on the new form of Christ.
Lord, help me to realize that I no longer exist in my old form but instead should take on your form.