[TheRealThing]

So for example, eating shellfish and pork, is an abomination to God, and once you get saved they are ok to consume?

Old Testament rules are different than New Testament rules. The reason being that in the OT, men looked forward to the coming of Christ, while in the NT, men look backward to the coming of Christ. This distinction is why the veil of the Holy of Holies was rent in twain by the God Himself at the time of Jesus' death, no longer would man need to go through a priest to make oblations to God in their name. From that day forward men would have open access to the throne of God through His Son, who had died that day to reconcile the sin gulf between God and man, which was created by Adam's fall. Jesus is the sin eraser, the capitulation of sin.

Therefore, where man had to temporarily cover his sin once a year through the offering of a blood sacrifice to God, and further to tithe and do all the other things commanded of God for the OT saints such as not eating or drinking certain things. New Testament saints have been set free of the law because of the permanent blood sacrifice of God's own Son that doesn't just hide man's sin, it washes away sin forever. This was something that God had to make clear to Peter in Acts 10:9-16 (KJV) 9 On the morrow, as they went on their journey, and drew nigh unto the city, Peter went up upon the housetop to pray about the sixth hour:
10 And he became very hungry, and would have eaten: but while they made ready, he fell into a trance,
11 And saw heaven opened, and a certain vessel descending unto him, as it had been a great sheet knit at the four corners, and let down to the earth:
12 Wherein were all manner of fourfooted beasts of the earth, and wild beasts, and creeping things, and fowls of the air.
13 And there came a voice to him, Rise, Peter; kill, and eat.
14 But Peter said, Not so, Lord; for I have never eaten any thing that is common or unclean.
15 And the voice spake unto him again the second time, What God hath cleansed, that call not thou common.
16 This was done thrice: and the vessel was received up again into heaven.

It was hard for man to give up the rites and ceremony to which they had become so accustomed. It's much easier to make a yearly sacrifice or not eat something particular than to live the life that he and other Christians would soon have to face. Don't forget, tradition has it that he would be crucified upside down. Others would be stoned, sawn in half, eaten by lions etc.