Never used in the New Testament, as in the Septuagint, of the mere physical organ, though sometimes of the vigor and sense of physical life (Act 14:17; Jam 5:5; Luk 21:34). Generally, the center of our complex being - physical, moral, spiritual, and intellectual. See on Mar 12:30. The immediate organ by which man lives his personal life, and where that entire personal life concentrates itself. It is thus used sometimes as parallel to ψυχηÌ, the individual life, and to πνεῦμα the principle of life, which manifests itself in the ψυχηÌ. Strictly, καÏδιÌα is the immediate organ of ψυχηÌ, occupying a mediating position between it and πνεῦμα. In the heart (καÏδιÌα) the spirit (πνεῦμα), which is the distinctive principle of the life or soul (ψυχηÌ), has the seat of its activity.
Emotions of joy or sorrow are thus ascribed both to the heart and to the soul. Compare Joh 14:27, “Let not your heart (καÏδιαÌ) be troubled;†and Joh 12:27, “Now is my soul (ψυχηÌ) troubled.†The heart is the focus of the religious life (Mat 22:37; Luk 6:45; 2Ti 2:22). It is the sphere of the operation of grace (Mat 13:19; Luk 8:15; Luk 24:32; Act 2:37; Rom 10:9, Rom 10:10). Also of the opposite principle (Joh 13:2; Act 5:3). Used also as the seat of the understanding; the faculty of intelligence as applied to divine things (Mat 13:15; Rom 1:21; Mar 8:17).
Ye believe - believe also (πιστευÌετε καὶ πιστευÌετε)
The verbs may be taken either as indicatives or as imperatives. Thus we may render: ye believe in God, ye believe also in me; or, believe in God and ye believe in me; or, believe in God and believe in me; or again, as A.V. The third of these renderings corresponds best with the hortatory character of the discourse.