Numbers 14:19, "Pardon the iniquity of this people, I pray, according to the greatness of Your mercy, just as You have forgiven this people, from Egypt even until now.”
The greatness of God's mercy is what we lean on. We are not leaning on the fitness of man. The Israelites deserved destruction, and so do we [vs12]. When we lean upon God for others in intercession, we're not pleading the greatness of our love or worthiness. We're dependent upon the greatness of God's mercy to glorify his name.
Ask God to glorify himself in saving sinners, and you'll have hope. The greatness of God must be used to get results.
First, "Pardon." We want the Lord to pardon people. We can see their faults, but we want God to do something for them that they don't deserve, according to his goodness. We want him to FORGIVE THEIR SIN, because it is great. Psalms 25:11, "For your name's sake, O LORD, pardon my guilt, for it is great."
Love doesn't merely see the sins of others; it wants God to help in the mightiest way. Too much preaching is angry. Too much is straightening out the sinner, but no forgiveness is proclaimed. Too much is without love and compassion. Too much is ignorant of full acceptance with God. Too much lacks what it takes for him to be merciful, which is forgiveness, pure and simple: The sinner is not punished, and he's blessed! Romans 4:8, "blessed is the man against whom the Lord will not count his sin."
Secondly, prayer. Moses said, "I pray." Prayer accesses God, and it works. Ephesians 2:18, "For through [Christ] we both [Jew and Gentile] have access by one Spirit to the Father." Prayer communes with him, and gets things from him. Prayer receives the blessing that can be gotten no other way. Hyper Calvinism says prayer is not necessary, because God has ordains. The Bible teaches prayer is how we get ordained things, and without prayer, many things do not come.
We ought to be mighty in prayer, because of confidence that we are heard [1 John 5:14-15]. Jesus made the way, and even the tiniest prayer is answered. It's not the length, it's the faith. It's bringing him ALL OF OUR NEEDS, and wrestling assurance of the blessing. It's obtaining mercy that we need.
Moses prayed, because he loved the people! A church that makes intercession for the community will be used. They persevere, because they love people. They want God's blessing on others. It is not to build up self. It's not to have numbers. This is asking amiss [James 4:4]! It's for God's glory in compassion. God uses people who pray for others, because they care and rely on him.
Thirdly, God's mercy is great. "According to the greatness of your mercy." It is greater than the mountains of sins. It is greater than the greatest evil [Acts 2:24]. It is as high as the heavens, and it is infinite. It washes sins away, and forgives transgressions. It receives people who ought to be destroyed.
We ought to know much about mercy, because he pours it upon us. Over and over, come to him filthy, and SEE HIM forgive and cleanse. Then, you'll know he can do great things for others.
Do not bind his compassion, but plead with God. Let his greatness lead you. Lay in agony before him. Do not merely let people die.
God's mercy is so great that he'll save people we pray for. He gives believing spouses. He saves our children and friends. Wrestle with him, dear saints, according to the greatness of God. Don't look at people as unsavable. Don't think that he's unwilling. He told us to pray, and he has used it mightily.
True, Israel was only physically spared, but it's a picture. He's showing us intercession works and prevails. Previously Moses pleaded his own love [Ex 32:32-33]. Now, he pleads God's love.
Finally, if we make intercession, then we are a successful church; it is a high fruit of love!