“With man this is impossible” means Salvation is impossible with man because man is limited. Man cannot deliver himself from the consequences of sin which leads to death and separation from God.
The bible recorded that the righteousness of man is as a filthy rag before God. (Isaiah 64:4) “But we are all as an unclean thing, and all our righteousnesses are as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.” It is difficult for man to resist the earthly things that comes with wealth unless the Spirit of God dominates such hearts
Righteousness comes ONLY from Christ and not through our good works. Our good works is not enough to take us to heaven. The only ticket to heaven is Salvation (Rom 10:8-10) says “That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation