Scripture exhorts us, “O, that today you would hear His voice, do not harden your hearts!” (Ps 95:7-8; Heb 3:7-8). Occasionally, that verse appears as a refrain to the Responsorial Psalm at Mass. For those who pray the Liturgy of the Hours, Morning Prayer usually begins with Psalm 95.

Why not “harden your hearts”? Because it turns us from God. When God warns us not to “harden your hearts” he also cites “as at Meribah, as in the day of Massa in the desert” (Ps 95:8). What is that all about?

When the Israelites arrived at Meribah during their sojourn across Sinai, they were once again grumbling and complaining, this time about lack of water. Now lack of water is serious business, especially in a desert. But lack of faith is also serious business, and the Israelites had demonstrated more than their share of its dearth. Remember, these people had witnessed how God, “with an outstretched arm and with mighty acts of judgment” (Ex 6:6) had freed the Hebrews from slavery and made a covenant with them. They had seen the plagues that befell Egypt. They saw how God rescued them at the Red Sea. They ate “bread from heaven” in the form of manna, and meat in the form of quail. God had repeatedly worked “signs and wonders” as proofs of His fidelity. Given what they had seen, why would they expect God to abandon them at Meribah?

We are bodily-spiritual creatures, and the sensible makes a huge impression on us. So huge that it often makes us stupid, reducing our horizons from great signs and wonders to where’s the next drink coming from? The pressure of that “practicality” is often the test of faith because it’s often where we discard it in favor of our own “control” and our own anxieties.

Meribah was a great test of faith, one even for Moses. God told Moses to “command the rock to yield its waters” (Nm 20:8). Moses did but, just in case, even he struck the rock twice with his staff. Was he making sure there was a crack for the liquid stream? Or was there a crack in his own faith, even though he had looked upon the Divine One and lived? This is why God tells Moses that, because of his lack of faith, he would ultimately not lead the Israelites into the Promised Land (Nm 20:12).

God wants us to have faith. Not 50% faith. Not 75% faith. Not even Ivory Soap 99 & 44/100% pure faith. God wants it all. It’s why we pray, “Lord, I believe; help my unbelief!” (Mk 9:24)

Let us not forget that whatever good we do begins first with God. The inspiration to do good is always God’s initiative. If that wasn’t true, we wouldn’t need Jesus; we could save ourselves. Our nature is fallen because of sin. It was God who took the initiative — all the way back in Eden (Gen 3:15) — to promise a Redeemer. Jesus as Redeemer makes available to us God’s grace. But God’s grace does not mean that “one-shot-fixes-all” and we can then just go about “doing good” all by ourselves. No, our salvation is always a finely choreographed dance in which God always leads. When today we hear His Voice — His Holy Spirit — we receive God’s actual grace, inspiring us to do something good. But God’s inspiration is not compulsive. Our free will also has to agree to follow that inspiration’s lead. As the Russian Orthodox monk Teofan the Recluse put it, grace is like an alarm clock. It wakes us up and makes us alert. But we still have to decide to get out of bed.

So, the good we do is first of all God’s grace. Grace, by definition, is gratis: it is a gift, not an entitlement. God offers His grace in history, i.e., in a concrete moment, amidst a concrete set of circumstances, in response to a concrete situation. What we do with God’s free gift is our choice, but that doesn’t mean all choices are equal. The child whose response to a gift is to turn up his nose, to complain ‘I don’t want it” or “I don’t want it now!” is a spoiled brat. He needs disciplinary correction because he doesn’t know how to relate to other people, especially persons freely giving him something good. Extrapolate that to the realm of the Divine. God did not have to redeem humanity, period. He did so out of Love (I J 4:8) — that is, out of Himself. Sure, we can turn Love down, but not without consequences.

When today “we hear His voice,” we hear and experience what He wants to do to make us holy. We experience actual grace which, as long as we pose no obstacle but cooperate with it, can lead us to sanctifying grace. But that means “hardening not your heart,” not resisting God, not playing deaf and dumb, not putting Him off.

After all, if we take history seriously, the moment matters. The German Redemptorist Bernard Häring liked to observe that the Greeks had two words for time: chronos and kairos. Chronos is the time that we measure, that goes by. Kairos, however, is “the moment” — the unrepeatable moment in history where “opportunity presents itself”; in the case of the spiritual life, this takes the form of grace. We all identify moments in our lives that were turning points, that made us what we are. Those are moments of God’s grace and our response (or non-response). They are more frequent than we reckon. And, as the saying goes, “opportunity doesn’t knock twice” because every moment is unique and unrepeatable. So, if God is calling you now, shouldn’t you answer?

Yes, God is merciful. Yes, God looks for the lost sheep. Yes, God hires the laborer at 9 am and 5 pm. But God doesn’t have to do that, and to put Him off out of expectation of one’s later convenience is in fact a sin. It’s called presumption, i.e., expecting God to do for you tomorrow what He is asking you to do today. This is a sin against piety, the gift that teaches us to recognize who God is, who we are, and what’s the difference.

The danger of such behavior is, of course, the unforgivable “sin against the Holy Spirit” (Mt 12:31-32), or final impenitence. It’s unforgivable because if we keep hardening our hearts to God, we either grow deaf to His call or run out of time to respond to it.