Our faith has no “worthiness”, but it is given as a gift of the Holy Spirit in order to be “an instrument with which we embrace Christ our righteousness”. Being only an instrument, faith is simply the means by which we are justified, not the ground. This is solely Christ and His righteousness. This was what Paul was saying to the Romans so many centuries ago in Romans 4.4-5. He reiterates that if we try to earn our salvation through strict obedience or even in the more pious term today of “covenant faithfulness”, we will get what we deserve. Our wages will be on the basis of what we did, whether heaven or hell.
On the contrary, Paul said that, if we trust in the God who justifies the ungodly, that is, the one who is stripped of his self-righteous works, naked and sin-stained in unrighteousness, we would be declared righteous. Faith, then, trusts in another, as it is only as good as its object. Faith simply rests in the mercy of God who, because Christ was condemned in our place, can bestow salvation upon us. It is amazing how simple this is. We either save ourselves or we are saved by another.
From: With Heart and Mouth: An Exposition of the Belgic Confession by Daniel R. Hyde (Grandville: Reformed Fellowship, Inc., 2008), p. 299.