From Joe Mullen

A And he said unto Moses, Come up unto the LORD, thou, and Aaron, Nadab, and Abihu, and seventy of the elders of Israel;

B and worship ye afar off.

C 2 And Moses alone shall come near the LORD:

B’ but they shall not come nigh;

A’ neither shall the people go up with him.

Note: The instructions are reversed in the second arm of the chiasm, with Moses being presented as the sole mediator in the centre;  cp 1 Timothy 2:5.

vv15-18

A 15 And Moses went up into the mount,

B and a cloud covered the mount.

C 16 And the glory of the LORD abode upon mount Sinai,

D and the cloud covered it six days:

D’ and the seventh day he called unto Moses out of the midst of the cloud.

C’ 17 And the sight of the glory of the LORD was like devouring fire on the top of the mount in the eyes of the children of Israel.

B’ And Moses went into the midst of the cloud, and gat him up into the mount:

A’ 18 and Moses was in the mount forty days and forty nights.

Note: The sixth and seventh day match the creation pattern, as if God is creating the law and commandments for six days and is now resting on the seventh day by giving them to Moses to teach them to the people. This is the creation of Israel as a nation cp Isaiah 43:1.