Karma becomes powerful when there are many people gathered together. For example, if one hundred people all gather together with the intention to kill a sheep and they kill a sheep, everyone receives the negative karma of killing that sheep.
This means if a government makes the decision to go to war and they are supported by the people of that country, then each person will receive the karma of killing, however many people die. If one human being is killed, they will all receive the karma of killing one human being. If a thousand people are killed, they will all receive the karma of having killed a thousand people.
Without the support of other people, if one person kills one sheep, then only that person receives the negative karma of having killed the sheep. Comparing which karma is more powerful, the previous instance, where so many people had the same intention and killed one sheep, is more powerful. Just one person killing a sheep is less powerful.
Similarly, if one hundred people build a stupa or just one person builds a stupa, the merit received is the same, but the first situation is more powerful than if only one person builds the stupa.
Similarly, the karma of one Sangha1 reciting a sutra in a temple or room alone, compared to reciting a sutra with all the assembly of Sangha present, the latter one—reciting a sutra with all the Sangha—is much more powerful. This applies to reciting prayers like Lama Chöpa alone in one’s own room or in the temple, or practicing it with a group. Reciting in a group is more powerful. The more people there are supporting the practice, the more powerful it becomes.
When the karma is more powerful, the result comes more quickly, whether it’s a project or realization. This is not mentioned in all the lam-rims, but it’s mentioned in the Kadampa thought transformation teachings.
1 Literally gen-dun: “intending virtue”.