Jeremiah 32:39
And I will give them one heart, and one way, that they may fear me for ever, for the good of them, and of their children after them: And I will give them one heart, and one way, that they may fear me for ever, for the good of them, and of their children after them:
Even with Jerusalem about to fall and the people about to go into exile, the promise belongs to the enduring purpose to restore Israel. In that restoration God Himself gives the people one united heart and one faithful way of life. The gift is given so that they will reverence Him continually forever, for the good of themselves and for the good of their children after them.
The fear to be given is holy fear and reverence that keeps His honor and glory constantly in view. It is shown in cheerful obedience rendered by His blood-bought heritage, in gratitude inspired by His great love, and in firm, confident trust placed wholly in Him. The promise stands together with His everlasting covenant not to turn away from doing them good and to put His fear in their hearts so that they will not depart from Him. When fulfilled it brings the joy of Christ and His Spirit, making the people a blessing to others.