I was just poking around in Second Clement. Here is §3, in Lake's translation:

1. Seeing, then, that he has shewn such mercy towards us, first that we who are living do not sacrifice to the dead gods, and do not worship them, but through him know the father of truth, what is the true knowledge concerning him except that we should not deny him through whom we knew him?
2. And he himself also says, “Whosoever confessed me before men, I will confess him before my Father”;
3. this then is our reward, if we confess him through whom we were saved.
4. But how do we confess him? By doing what he says, and not disregarding his commandments, and honouring him not only with our lips, but “with all our heart and all our mind.”
5. And he says also in Isaiah, “This people honoureth me with their lips, but their heart is far from me.” (2Cl 3)

This is interesting to me because of the progression through references; the homilist here uses both OT and NT references to convey to his reader (hearer) the benefit of confessing Christ, who has saved us from certain death  (recall §1 of Second Clement), before men. If Christians confess Christ before others, then Christ will confess us before his Father.

And how do we confess him? The homilist tells us we confess him in our words and in our actions:  "By doing what he says, and not disregarding his commandments, and honouring him not only with our lips, but 'with all our heart and all our mind.' "

Then comes the quote from Isaiah (actually introduced as a quote from Isaiah ... that's nice). And then we go into §4, where the homilist urges Christians to not be like the people Isaiah was describing:

1. Let us, then, not merely call him Lord, for this will not save us.
2. For he says, “Not everyone that saith to me Lord, Lord, shall be saved, but he that doeth righteousness.”
3. So then, brethren, let us confess him in our deeds, by loving one another, by not committing adultery, nor speaking one against another, nor being jealous, but by being self-controlled, merciful, good; and we ought to sympathise with each other, and not to be lovers of money. By these deeds we confess him, and not by the opposite kind.
4. And we must not fear men rather than God.
5. For this reason, if you do these things, the Lord said, “If ye be gathered together with me in my bosom, and do not my commandments, I will cast you out, and will say to you, Depart from me, I know not whence ye are, ye workers of iniquity.” (2Cl 4)

Again, the application is simple: If the people that confessed with lips but not heart are far from the Lord, then we be must people that confess with lips and with heart. Thus we confess with our deeds, by adhering to the commands set before us (note the homilist's list sounds like Pauline lists of vice/virtue).

In this way we show that we do not fear men over God; for our actions reflect God's leading and commands. In this way, the homilist bases his teaching on both OT and NT passages and makes his teaching practical to those who will hear him.

The quotations in §4 are, according to Lake, likely from the Gospel of the Egyptians, though no real evidence for that is available.