Psalm 41:1-4 exemplifies this principle: God shows mercy to those who consider the poor, delivering them in trouble.

Psalm 112:4-6 describes the upright person blessed with light and stability, illustrating God's upright response to the upright.

Psalm 25:10 declares God's steadfast love and faithfulness to covenant-keepers — a clear parallel to the reciprocal treatment in Psalm 18:25.

Psalm 36:10 asks God to show steadfast love to the upright — directly echoing the reciprocal theme of Psalm 18:25.

Isaiah 57:2 promises peace and rest for the upright, directly fulfilling the promise that God shows himself upright to the upright.

Matthew 18:33-35 applies the same principle: forgiveness received as we forgive; unmerciful servant faces judgment — a direct parallel.

Luke 6:35-38 explicitly states 'with the measure you use it will be measured to you' — the same reciprocal principle as here.

1 Samuel 26:24 illustrates the principle: David spares Saul and prays for reciprocal mercy from God — a direct application of Psalm 18:25.

Matthew 5:7 promises mercy to the merciful — a direct New Testament parallel to the reciprocal mercy principle in Psalm 18:25.

Matthew 7:2 applies the same reciprocal principle to human judgment: the measure you use will be measured back to you.

Luke 6:38 extends the principle to giving: with the measure you use, it will be measured back to you, echoing the reciprocal nature of God's dealings.

Isaiah 58:7 defines merciful acts — feeding hungry, clothing naked — which are the kind of mercy that invites God's mercy per this principle.

2 Timothy 1:16 prays for mercy on Onesiphorus who showed mercy, illustrating the principle that the merciful receive mercy.