Point B is on IC1 and point G is on IC2.
At B, a consumer gets OA, OS combination (or bundles) of goods.
At C, a consumer gets OA, OT combination of goods.
Certainly OT > OS. Implying that at C a consumer gets more of Good-1 and the same amount of Good-2 as at B. We know according to his monotonic preferences, a rational consumer gets more satisfaction from more of good. Accordingly, C on IC2 (or any other point on IC2) must offer the consumer greater satisfaction than B on IC1 (or any other point on IC1). Hence, it is proved that a higher IC implies a higher level of satisfaction.