Many ask this question when they do not understand the difference between a sacrifice for sin and a sacrifice for proof.
When the Lord Jesus went to the cross to sacrifice for us, His sacrifice was for our sins. He was the Lamb offered by the Father as our Substitute. Since then, it is no longer necessary to sacrifice because of sins. All you have to do is believe, accept the Father’s Offering and live in obedience to His Word to receive forgiveness, and consequently Salvation.
But, the sacrifice for sin was just one kind of sacrifice. There is no indication that Jesus abolished any other sacrifices that prove our faith. On the contrary, we see the same tests of faith being required and practiced in the New Testament as well. For example, the rich young man (Luke 18.22), Zacchaeus (Luke 19.8), the Early Church (Acts 4.34) and Paul’s advice (2 Corinthians 8.8), among many others.
When God asked Abraham for his son Isaac as a sacrifice, it wasn’t because Abraham was in sin. This was proof of his faith. In the same way, he asked Gideon for his father’s second bull. This wasn’t a sacrifice for sin, but proof of his dependence on Him.
This kind of sacrifice, to prove a person’s faith, was never abolished. It is as necessary and real today as it has been since the origin of Genesis.