The two ideas seem in conflict, don’t they?
I don't think so. One thing that leads me to think that His sacrifice was sufficient for everyone is hypothetically imagining what would happen if God decided to save one more person beyond the original plan. Would Jesus then have to do something more to cover him? Obviously not. However, since we know that His sacrifice was only efficacious for some we have to decide whether that was by plan, or is that just the way it turned out based on man's decisions. The Reformed believe that God has a fully comprehensive plan for the universe and He is executing that plan flawlessly within time. If that is true, and if God is free to decide whom He wants to be with Him in Heaven, then it MUST have been by design that the sacrifice was only intended to be efficacious for some, i.e. only FOR some.
God's plan governs to whom the sacrifice applies without regard to how powerful the sacrifice actually was.
AMEN! Very well stated.
"The LORD of hosts hath sworn, saying, Surely as I have thought, so shall it come to pass; and as I have purposed, so shall it stand: That I will break the Assyrian in my land, and upon my mountains tread him under foot: then shall his yoke depart from off them, and his burden depart from off their shoulders. This is the purpose that is purposed upon the whole earth: and this is the hand that is stretched out upon all the nations. For the LORD of hosts hath purposed, and who shall disannul it? and his hand is stretched out, and who shall turn it back?" -- Isaiah 14:24-27 "For the promise is unto you, and to your children, and to all that are afar off, even as many as the LORD our God shall call." -- Acts 2:39