Charles Ellicott Commentary Exodus 20:6

"and showing lovingkindness unto thousands of them that love me and keep my commandments." — Exodus 20:6 (ASV)

Shewing mercy unto thousands. —Rather, to the thousandth generation, as is distinctly expressed in Deuteronomy 7:9. God’s mercy infinitely transcends His righteous anger. Sin is visited on three, or at most four, generations. Righteousness is remembered, and benefits descendants, forever.