Behold, God is mine helper: the Lord is with them that uphold my soul.
Behold. He already, with the eye of faith, sees God advancing as his "helper," though to the eye of sense nothing presented itself but destruction on every side.
The Lord is with them that uphold my soul in opposition to the "oppressors," who "seek after my soul" (Psalms 54:4). Compare the phrase with Psalms 118:7. David supposes two parties his opponents and his helpers: the Lord constituted the latter party (Psalms 55:18, "there were many with me"). He does not mean that he had other helpers besides the Lord (cf. the phrase, Judges 11:35).