Stephen was a Christian man full of faith and power, and he was serving tables in obedience to God’s call (Acts 6). I have heard ministry referred to as “the highest calling.” But there is no one particular “highest calling”.
If you are a Christian, whatever God has called you to do is your highest calling. If it is serving tables, then do it as unto the Lord. The Bible encourages Christians: “And whatever you do in word of deed, do all in the name of the Lord Jesus” (Col.3:17). I am what I am for the Lord because of His calling upon my life. It is important that I be faithful to His call.