Our heart is linked to our spirit, for our conscience, which is a function of our spirit (Rom. 9:1), is also a function of our heart (Heb. 10:22). Thus, to love and serve God with all our heart and soul indicates that we love and serve Him also with our spirit (Rom. 1:9). Furthermore, according to 6:5 we are to love Him also with all our might, that is, with our physical strength. See Mark 12:28-30 and note Mark 12:301.