not ... secret - not like the heathen oracles which gave their responses from dark caverns, with studied obscurity (Isa 48:16). Christ plainly quotes these words, thereby identifying Himself with Jehovah (Joh 18:20).
I said not ... Seek ... in vain - When I commanded you to seek Me (Jehovah did so, Isa 45:11, “Ask Me,” etc.), it was not in order that ye might be sent empty away (Deu 32:47). Especially in Israel’s time of trial, God’s interposition, in behalf of Zion hereafter, is expressly stated as about to be the answer to prayer (Isa 62:6, Isa 62:7-10; Psa 102:13-17, Psa 102:19-21). So in the case of all believers, the spiritual Israel.
righteousness - that which is veracious: not in the equivocal terms of heathen responses, fitly symbolized by the “dark places” from which they were uttered.