Charles Spurgeon Commentary Romans 3:4

"God forbid: yea, let God be found true, but every man a liar; as it is written, That thou mightest be justified in thy words, And mightest prevail when thou comest into judgment." — Romans 3:4 (ASV)

God forbid: yea, let God be true, but every man a liar; as it is written, that thou mightest be justified in thy sayings, and mightest overcome when thou art judged.

However faithless men might be, God was still true and faithful.

Paul quotes the Septuagint, which in this way renders David's words.

God forbid: yea, let God be true, but every man a liar; as it is written, That thou mightest be justified in thy sayings, and mightest overcome when thou art judged.

Whatever men did under the old law, however faithless they might be, God was true and faithful still.