if indeed you have tasted that the Lord is gracious:
This seems to refer to Psalms 34:8: O taste and see that the Lord is good; γευσασθε και ιδετε οτι χρηστος ο κυριος, Sept. And there is still a reference to the sucking child that, having once tasted its mother's milk, ever after desires and longs for it. As they were born of God, and had tasted his goodness, they would naturally desire the same pure unadulterated milk of the word.