The Buddha explains the benefits of cultivating loving-kindness compared to giving donations.

At Sāvatthi.

"Bhikkhus, if someone were to give a donation (the act of giving or donating, with an intention to give [dāna]) of a hundred pots [of food] in the morning, a hundred pots of food at noon, and a hundred pots of food in the evening, and if someone else were to cultivate a mind of loving-kindness (friendly heart, kind mind, benevolent mind [mettācitta]) even for the brief moment it takes to milk a cow, whether in the morning, at noon, or in the evening — this [cultivation of loving-kindness] would yield far greater fruit than those givings.

Therefore, bhikkhus, you should train yourselves thus: 'Our release of mind (mental liberation, emancipation of heart, a meditation attainment [cetovimutti]) through loving-kindness will be developed, practiced often, made a vehicle, made a basis, firmly established, nurtured, and resolutely undertaken (fully engaged with, energetically taken up [susamāraddha]).' Thus, bhikkhus, you should train yourselves."

Related Teachings:

Five ways to remove arisen resentment (AN 5.161) - 1) loving-kindness, 2) compassion, 3) equanimity, 4) disregarding and non-attention, 5) reflection on kamma.

11 Benefits of practicing Loving-Kindness (AN 11.15) - from sleeping with ease to dying unconfused to going to the Brahma world.

Verses on Loving-Kindness | Metta Sutta (Snp 1.8) - This Metta Sutta offers a practical way to overcome any negative states of mind and root them in contentment, good-will and harmlessness.