Jamieson, Fausset and Brown on Isaiah 57:11

11. Israel wished not to seem altogether to have denied God. Therefore they "lied" to Him. God asks, Why dost thou do so? "Whom dost thou fear? Certainly not Me; for thou hast not remembered Me." Translate, "seeing that thou hast not remembered Me."

laid it to ... heart--rather, "nor hast Me at heart"; hast no regard for Me; and that, because I have been long silent and have not punished thee. Literally, "Have I not held My peace, and that for long? and so thou fearest Me not" (Psa 50:21; Ec 8:11). It would be better openly to renounce God, than to "flatter Him" with lies of false professions (Psa 78:36) [Ludovicus De Dieu]. However, Is 51:12, 13 favors English Version of the whole verse; God's "silent" long-suffering, which was intended to lead them to repentance, caused them "not to fear Him" (Ro 2:4, 5).