The greatest and first...

Jesus answered:" the first is, 'Hear, O Isreal, Jehovah our God is one Jehovah, and you must love Jehovah your God with your whole heart, and with your whole soul, and with your whole mind and with your whole strength.' (Mark 12:29,30)

heart:  feelings, desires, in most thoughts, fervently desire to please Him.

soul:  our whole being; the life we possess; our assets and our means to serve and praise Him.
            
mind:  devotion not blind; have come to know Jehovah's qualities, standards and His purposes.

strength:  with all our vital force, a life time of service.