A missionary is not sent by an agency, though it certainly had a part in the process and the accountability is usually a positive necessity. A missionary is also not sent by the church, though it acts to affirm the will of the One who sends and is an essential channel for the process. A missionary is sent by God … or he (she) simply is not sent and the proof of this sending relationship is seen in his (her) worship.
He answered, “I will certainly be with you, and this will be the sign to you that I have sent you: when you bring the people out of Egypt, you will all worship God at this mountain.” – Exodus 3:12
It is a normal practice for a Western missionary to be appointed for overseas service through an outside agency. These agencies often (should) act as intermediaries between the local churches and the needs overseas and (in that role) are often able to provide important logistical support as well as experienced oversight. Yet, in the context of such a system, it is also possible for a missionary to become confused about who actually does the sending.
Moses worshiped GOD on the mountain. He did not worship Israel, the priesthood, or the tabernacle. While a missionary should honor the church’s and the agency’s authority, his first allegiance belongs to the ONE who sent. Honor and respect all parties in the sending, but worship HIM.
Then I heard the voice of the Lord saying: Who should I send? Who will go for Us? I said: Here I am. Send me. – YHWH to Isaiah (6:8)