But Jesus seems to endorse the enirety of the Old Testament law:
For truly, I say to you, till heaven and earth pass away, not an iota, not a dot, will pass from the law until all is accomplished. Whoever then relaxes one of the least of these commandments and teaches men so, shall be called least in the Kingdom of heaven, but he who does them and teaches them shall be called great in the kingdom of heaven. For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven. - Mathew 5:18-19
It seems to me that true Christians must obey the OT law in order to get into heaven, am I wrong?
Indeed you are wrong here as John 8 records:
1 But Jesus went to
(A)the Mount of Olives.
2 Early in the morning He came again into the temple, and all the people were coming to Him; and
(B)He sat down and
began to teach them.
3 The scribes and the Pharisees *brought a woman caught in adultery, and having set her in the center
of the court,
4 they *said to Him, Teacher, this woman has been caught in adultery, in the very act.
5 Now in the Law
(C)Moses commanded us to stone such women; what then do You say?
6 They were saying this,
(D)testing Him,
(E)so that they might have grounds for accusing Him. But Jesus stooped down and with His finger wrote on the ground.
7 But when they persisted in asking Him,
(F)He straightened up, and said to them,
(G)He who is without sin among you, let him
be the (H)first to throw a stone at her.
8 Again He stooped down and wrote on the ground.
9 When they heard it, they
began to go out one by one, beginning with the older ones, and He was left alone, and the woman, where she was, in the center
of the court.
10 (I)Straightening up, Jesus said to her, Woman, where are they? Did no one condemn you?
11 She said, No one,
[a]Lord. And Jesus said,
(J)I do not condemn you, either. Go. From now on
(K)sin no more.]