Jn 6:28-29, Jn 14:6, Jn 6: 39-40, Col 1:9
It is God's work to believe that Christ, the one sent by God, is Jesus. Also, when we believe in Jesus as the Christ, we can come to know God. (Eph 1:17, Jn 6:28-29, Jn 14:6)
Eph 1:17 That the God of our Lord Jesus Christ, the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him:
Jn 6:28 Then said they unto him, What shall we do, that we might work the works of God? 29 Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent.
Jn 14:6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.
Also, the reason God has called us is to save those whom God has entrusted to us. (Eph 1:18, Jn 6:39-40, Col 1:9)
Eph 1:18 The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints,
Jn 6:39 And this is the Father's will which hath sent me, that of all which he hath given me I should lose nothing, but should raise it up again at the last day. 40 And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.
Col 1:9 For this cause we also, since the day we heard it, do not cease to pray for you, and to desire that ye might be filled with the knowledge of his will in all wisdom and spiritual understanding;