In this model Christ did PART of salvation for PART of mankind.

This model assumes that when Jesus died on the cross he only paid for the sins of PART of mankind.  Furthermore, suppose he only did PART of the work so that individuals must meet an additional condition to be saved.

For an extreme example, suppose that Mother Teresa is not within the PART of mankind that Jesus forgave.  Or suppose she misses the condition needed for salvation.  Then even she will not be saved from eternal damnation in the end, regardless of her great goodness.  By way of contrast, suppose Hitler is within the PART of mankind that Jesus chose to forgive.  And suppose he somehow meets the condition needed for salvation.  Then he will be saved from damnation to eternal life in the end, regardless of his great evil.

Thankfully, this view disagrees with I John 2:1-2 (WEB) which explains that Jesus did die for ALL mankind.

1) My little children, I write these things to you so that you may not sin. If anyone sins, we have a Counselor with the Father, Jesus Christ, the righteous. 2) And he is the atoning sacrifice for our sins, and not for ours only, but also for the whole world.

This view also disagrees with Ephesians 2:8-9 (WEB), which explains that we are saved by grace apart from any work.

8) For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, 9) not of works, that no one would boast.

Therefore, the PART-for-PART model of salvation is rejected by nearly all followers of Christ.